GERANIACEAE, LEGUMINOSAE, ONAGRACEAE, ETC.

The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom by Charles Darwin, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. GERANIACEAE, LEGUMINOSAE, ONAGRACEAE, ETC.

GERANIACEAE, LEGUMINOSAE, ONAGRACEAE, ETC

13. GERANIACEAE.—Pelargonium zonale.

This plant, as a general rule, is strongly proterandrous, and is therefore adapted for cross-fertilisation by the aid of insects. (5/1. Mr. J. Denny, a great raiser of new varieties of pelargoniums, after stating that this species is proterandrous, adds ‘The Florist and Pomologist’ January 1872 page 11, “there are some varieties, especially those with petals of a pink colour, or which possess a weakly constitution, where the pistil expands as soon as or even before the pollen-bag bursts, and in which also the pistil is frequently short, so when it expands it is smothered as it were by the bursting anthers; these varieties are great seeders, each pip being fertilised by its own pollen. I would instance Christine as an example of this fact.” We have here an interesting case of variability in an important functional point.) Some flowers on a common scarlet variety were self-fertilised, and other flowers were crossed with pollen from another plant; but no sooner had I done so, than I remembered that these plants had been propagated by cuttings from the same stock, and were therefore parts in a strict sense of the same individual. Nevertheless, having made the cross I resolved to save the seeds, which, after germinating on sand, were planted on the opposite sides of three pots. In one pot the quasi-crossed plant was very soon and ever afterwards taller and finer than the self-fertilised. In the two other pots the seedlings on both sides were for a time exactly equal; but when the self-fertilised plants were about 10 inches in height, they surpassed their antagonists by a little, and ever afterwards showed a more decided and increasing advantage; so that the self-fertilised plants, taken altogether, were somewhat superior to the quasi-crossed plants. In this case, as in that of the Origanum, if individuals which have been asexually propagated from the same stock, and which have been long subjected to the same conditions, are crossed, no advantage whatever is gained.

Several flowers on another plant of the same variety were fertilised with pollen from the younger flowers on the same plant, so as to avoid using the old and long-shed pollen from the same flower, as I thought that this latter might be less efficient than fresh pollen. Other flowers on the same plant were crossed with fresh pollen from a plant which, although closely similar, was known to have arisen as a distinct seedling. The self-fertilised seeds germinated rather before the others; but as soon as I got equal pairs they were planted on the opposite sides of four pots.

TABLE 5/49. Pelargonium zonale.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 22 3/8 : 25 5/8. Pot 1 : 19 6/8 : 12 4/8.

Pot 2 : 15 : 19 6/8. Pot 2 : 12 2/8 : 22 3/8.

Pot 3 : 30 5/8 : 19 4/8. Pot 3 : 18 4/8 : 7 4/8.

Pot 4 : 38 : 9 1/8.

Total : 156.50 : 116.38.

When the two lots of seedlings were between 4 and 5 inches in height they were equal, excepting in Pot 4, in which the crossed plant was much the tallest. When between 11 and 14 inches in height, they were measured to the tips of their uppermost leaves; the crossed averaged 13.46, and the self-fertilised 11.07 inches in height, or as 100 to 82. Five months later they were again measured in the same manner, and the results are given in Table 5/49.

The seven crossed plants now averaged 22.35, and the seven self-fertilised 16.62 inches in height, or as 100 to 74. But from the great inequality of the several plants, the result is less trustworthy than in most other cases. In Pot 2 the two self-fertilised plants always had an advantage, except whilst quite young over the two crossed plants.

As I wished to ascertain how these plants would behave during a second growth, they were cut down close to the ground whilst growing freely. The crossed plants now showed their superiority in another way, for only one out of the seven was killed by the operation, whilst three of the self-fertilised plants never recovered. There was, therefore, no use in keeping any of the plants excepting those in Pots 1 and 3; and in the following year the crossed plants in these two pots showed during their second growth nearly the same relative superiority over the self-fertilised plants as before.

Tropaeolum minus.

The flowers are proterandrous, and are manifestly adapted for cross-fertilisation by insects, as shown by Sprengel and Delpino. Twelve flowers on some plants growing out of doors were crossed with pollen from a distinct plant and produced eleven capsules, containing altogether twenty-four good seeds. Eighteen flowers were fertilised with their own pollen and produced only eleven capsules, containing twenty-two good seeds; so that a much larger proportion of the crossed than of the self-fertilised flowers produced capsules, and the crossed capsules contained rather more seed than the self-fertilised in the ratio of 100 to 92. The seeds from the self-fertilised capsules were however the heavier of the two, in the ratio of 100 to 87.

Seeds in an equal state of germination were planted on the opposite sides of four pots, but only the two tallest plants on each side of each pot were measured to the tops of their stems. The pots were placed in the greenhouse, and the plants trained up sticks, so that they ascended to an unusual height. In three of the pots the crossed plants flowered first, but in the fourth at the same time with the self-fertilised. When the seedlings were between 6 and 7 inches in height, the crossed began to show a slight advantage over their opponents. When grown to a considerable height the eight tallest crossed plants averaged 44.43, and the eight tallest self-fertilised plants 37.34 inches, or as 100 to 84. When their growth was completed they were again measured, as shown in Table 5/50.

TABLE 5/50. Tropaeolum minus.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 65 : 31. Pot 1 : 50 : 45.

Pot 2 : 69 : 42. Pot 2 : 35 : 45.

Pot 3 : 70 : 50 4/8. Pot 3 : 59 4/8 : 55 4/8.

Pot 4 : 61 4/8 : 37 4/8. Pot 4 : 57 4/8 : 61 4/8.

Total : 467.5 : 368.0.

The eight tallest crossed plants now averaged 58.43, and the eight tallest self-fertilised plants 46 inches in height, or as 100 to 79.

There was also a great difference in the fertility of the two lots which were left uncovered in the greenhouse. On the 17th of September the capsules from all the plants were gathered, and the seeds counted. The crossed plants yielded 243, whilst the same number of self-fertilised plants yielded only 155 seeds, or as 100 to 64.

Limnanthes douglasii.

Several flowers were crossed and self-fertilised in the usual manner, but there was no marked difference in the number of seeds which they yielded. A vast number of spontaneously self-fertilised capsules were also produced under the net. Seedlings were raised in five pots from the above seeds, and when the crossed were about 3 inches in height they showed a slight advantage over the self-fertilised. When double this height, the sixteen crossed and sixteen self-fertilised plants were measured to the tips of their leaves; the former averaged 7.3 inches, and the self-fertilised 6.07 inches in height, or as 100 to 83. In all the pots, excepting 4, a crossed plant flowered before any one of the self-fertilised plants. The plants, when fully grown, were again measured to the summits of their ripe capsules, with the result in Table 5/51.

TABLE 5/51. Limnanthes douglasii.

Heights of plants to the summits of their ripe capsules, measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 17 7/8 : 15 1/8. Pot 1 : 17 6/8 : 16 4/8. Pot 1 : 13 : 11.

Pot 2 : 20 : 14 4/8. Pot 2 : 22 : 15 6/8. Pot 2 : 21 : 16 1/8. Pot 2 : 18 4/8 : 17.

Pot 3 : 15 6/8 : 11 4/8. Pot 3 : 17 2/8 : 10 4/8. Pot 3 : 14 : 0.

Pot 4 : 20 4/8 : 13 4/8. Pot 4 : 14 : 13. Pot 4 : 18 : 12 2/8.

Pot 5 : 17 : 14 2/8. Pot 5 : 18 5/8 : 14 1/8. Pot 5 : 14 2/8 : 12 5/8.

Total : 279.50 : 207.75.

The sixteen crossed plants now averaged 17.46, and the fifteen (for one had died) self-fertilised plants 13.85 inches in height, or as 100 to 79. Mr. Galton considers that a higher ratio would be fairer, namely, 100 to 76. He made a graphical representation of the above measurements, and adds the words “very good” to the curvature thus formed. Both lots of plants produced an abundance of seed-capsules, and, as far as could be judged by the eye, there was no difference in their fertility.]

14. LEGUMINOSAE.

In this family I experimented on the following six genera, Lupinus, Phaseolus, Lathyrus, Pisum, Sarothamnus, and Ononis.

[Lupinus luteus. (5/2. The structure of the flowers of this plant, and their manner of fertilisation, have been described by H. Muller ‘Befruchtung’ etc. page 243. The flowers do not secrete free nectar, and bees generally visit them for their pollen. Mr. Farrer, however, remarks ‘Nature’ 1872 page 499, that “there is a cavity at the back and base of the vexillum, in which I have not been able to find nectar. But the bees, which constantly visit these flowers, certainly go to this cavity for what they want, and not to the staminal tube.”)

A few flowers were crossed with pollen from a distinct plant, but owing to the unfavourable season only two crossed seeds were produced. Nine seeds were saved from flowers spontaneously self-fertilised under a net, on the same plant which yielded the two crossed seeds. One of these crossed seeds was sown in a pot with two self-fertilised seeds on the opposite side; the latter came up between two and three days before the crossed seed. The second crossed seed was sown in like manner with two self-fertilised seeds on the opposite side; these latter also came up about a day before the crossed one. In both pots, therefore, the crossed seedlings from germinating later, were at first completely beaten by the self-fertilised; nevertheless, this state of things was afterwards completely reversed. The seeds were sown late in the autumn, and the pots, which were much too small, were kept in the greenhouse. The plants in consequence grew badly, and the self-fertilised suffered most in both pots. The two crossed plants when in flower during the following spring were 9 inches in height; one of the self-fertilised plants was 8, and the three others only 3 inches in height, being thus mere dwarfs. The two crossed plants produced thirteen pods, whilst the four self-fertilised plants produced only a single one. Some other self-fertilised plants which had been raised separately in larger pots produced several spontaneously self-fertilised pods under a net, and seeds from these were used in the following experiment.

CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.

The spontaneously self-fertilised seeds just mentioned, and crossed seeds obtained by intercrossing the two crossed plants of the last generation, after germinating on sand, were planted in pairs on the opposite sides of three large pots. When the seedlings were only 4 inches in height, the crossed had a slight advantage over their opponents. When grown to their full height, every one of the crossed plants exceeded its opponent in height. Nevertheless the self-fertilised plants in all three pots flowered before the crossed! The measurements are given in Table 5/52.

TABLE 5/52. Lupinus luteus.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 33 2/8 : 24 4/8. Pot 1 : 30 4/8 : 18 4/8. Pot 1 : 30 : 28.

Pot 2 : 29 4/8 : 26. Pot 2 : 30 : 25.

Pot 3 : 30 4/8 : 28. Pot 3 : 31 : 27 2/8. Pot 3 : 31 4/8 : 24 4/8.

Total : 246.25 : 201.75.

The eight crossed plants here average 30.78, and the eight self-fertilised 25.21 inches in height; or as 100 to 82. These plants were left uncovered in the greenhouse to set their pods, but they produced very few good ones, perhaps in part owing to few bees visiting them. The crossed plants produced nine pods, containing on an average 3.4 seeds, and the self-fertilised plants seven pods, containing on an average 3 seeds, so that the seeds from an equal number of plants were as 100 to 88.

Two other crossed seedlings, each with two self-fertilised seedlings on the opposite sides of the same large pot, were turned out of their pots early in the season, without being disturbed, into open ground of good quality. They were thus subjected to but little competition with one another, in comparison with the plants in the above three pots. In the autumn the two crossed plants were about 3 inches taller than the four self-fertilised plants; they looked also more vigorous and produced many more pods.

Two other crossed and self-fertilised seeds of the same lot, after germinating on sand, were planted on the opposite sides of a large pot, in which a Calceolaria had long been growing, and were therefore exposed to unfavourable conditions: the two crossed plants ultimately attained a height of 20 1/2 and 20 inches, whilst the two self-fertilised were only 18 and 9 1/2 inches high.

Lupinus pilosus.

From a series of accidents I was again unfortunate in obtaining a sufficient number of crossed seedlings; and the following results would not be worth giving, did they not strictly accord with those just given with respect to Lupinus luteus. I raised at first only a single crossed seedling, which was placed in competition with two self-fertilised ones on the opposite side of the same pot. These plants, without being disturbed, were soon afterwards turned into the open ground. By the autumn the crossed plant had grown to so large a size that it almost smothered the two self-fertilised plants, which were mere dwarfs; and the latter died without maturing a single pod. Several self-fertilised seeds had been planted at the same time separately in the open ground; and the two tallest of these were 33 and 32 inches, whereas the one crossed plant was 38 inches in height. This latter plant also produced many more pods than did any one of the self-fertilised plants, although growing separately. A few flowers on the one crossed plant were crossed with pollen from one of the self-fertilised plants, for I had no other crossed plant from which to obtain pollen. One of the self-fertilised plants having been covered by a net produced plenty of spontaneously self-fertilised pods.

CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.

From crossed and self-fertilised seeds obtained in the manner just described, I succeeded in raising to maturity only a pair of plants, which were kept in a pot in the greenhouse. The crossed plant grew to a height of 33 inches, and the self-fertilised to that of 26 1/2 inches. The former produced, whilst still kept in the greenhouse, eight pods, containing on an average 2.77 seeds; and the latter only two pods, containing on an average 2.5 seeds. The average height of the two crossed plants of the two generations taken together was 35.5, and that of the three self-fertilised plants of the same two generations 30.5; or as 100 to 86. (5/3. We here see that both Lupinus luteus and pilosus seed freely when insects are excluded; but Mr. Swale, of Christchurch, in New Zealand, informs me ‘Gardeners’ Chronicle’ 1858 page 828, that the garden varieties of the lupine are not there visited by any bees, and that they seed less freely than any other introduced leguminous plant, with the exception of red clover. He adds “I have, for amusement, during the summer, released the stamens with a pin, and a pod of seed has always rewarded me for my trouble, the adjoining flowers not so served having all proved blind.” I do not know to what species this statement refers.)

Phaseolus multiflorus.

This plant, the scarlet-runner of English gardeners and the Phaseolus coccineus of Lamarck, originally came from Mexico, as I am informed by Mr. Bentham. The flowers are so constructed that hive and humble-bees, which visit them incessantly, almost always alight on the left wing-petal, as they can best suck the nectar from this side. Their weight and movements depress the petal, and this causes the stigma to protrude from the spirally-wound keel, and a brush of hairs round the stigma pushes out the pollen before it. The pollen adheres to the head or proboscis of the bee which is at work, and is thus placed either on the stigma of the same flower, or is carried to another flower. (5/4. The flowers have been described by Delpino, and in an admirable manner by Mr. Farrer in the ‘Annals and Magazine of Natural History’ volume 2 4th series October 1868 page 256. My son Francis has explained ‘Nature’ January 8, 1874 page 189, the use of one peculiarity in their structure, namely, a little vertical projection on the single free stamen near its base, which seems placed as if to guard the entrance into the two nectar-holes in the staminal sheath. He shows that this projection prevents the bees reaching the nectar, unless they go to the left side of the flower, and it is absolutely necessary for cross-fertilisation that they should alight on the left wing-petal.) Several years ago I covered some plants under a large net, and these produced on one occasion about one-third, and on another occasion about one-eighth, of the number of pods which the same number of uncovered plants growing close alongside produced. (5/5. ‘Gardeners’ Chronicle’ 1857 page 725 and more especially ibid 1858 page 828. Also ‘Annals and Magazine of Natural History’ 3rd series volume 2 1858 page 462.) This lessened fertility was not caused by any injury from the net, as I moved the wing-petals of several protected flowers, in the same manner as bees do, and these produced remarkably fine pods. When the net was taken off, the flowers were immediately visited by bees, and it was interesting to observe how quickly the plants became covered with young pods. As the flowers are much frequented by Thrips, the self-fertilisation of most of the flowers under the net may have been due to the action of these minute insects. Dr. Ogle likewise covered up a large portion of a plant, and “out of a vast number of blossoms thus protected not a single one produced a pod, while the unprotected blossoms were for the most part fruitful.” Mr. Belt gives a more curious case; this plant grows well and flowers in Nicaragua; but as none of the native bees visit the flowers, not a single pod is ever produced. (5/6. Dr. Ogle ‘Popular Science Review’ 1870 page 168. Mr. Belt ‘The Naturalist in Nicaragua’ 1874 page 70. The latter author gives a case ‘Nature’ 1875 page 26, of a late crop of Phaseolus multiflorus near London which “was rendered barren” by the humble-bees cutting, as they frequently do, holes at the bases of the flowers instead of entering them in the proper manner.)

From the facts now given we may feel nearly sure that individuals of the same variety or of different varieties, if growing near each other and in flower at the same time, would intercross; but I cannot myself advance any direct evidence of such an occurrence, as only a single variety is commonly cultivated in England. I have, however, received an account from the Reverend W.A. Leighton, that plants raised by him from ordinary seed produced seeds differing in an extraordinary manner in colour and shape, leading to the belief that their parents must have been crossed. In France M. Fermond more than once planted close together varieties which ordinarily come true and which bear differently coloured flowers and seeds; and the offspring thus raised varied so greatly that there could hardly be a doubt that they had intercrossed. (5/7. ‘Fécondation chez les Végétaux’ 1859 pages 34-40. He adds that M. Villiers has described a spontaneous hybrid, which he calls Phaseolus coccineus hybridus, in the ‘Annales de la Soc. R. de Horticulture’ June 1844.) On the other hand, Professor H. Hoffman does not believe in the natural crossing of the varieties; for although seedlings raised from two varieties growing close together produced plants which yielded seeds of a mixed character, he found that this likewise occurred with plants separated by a space of from 40 to 150 paces from any other variety; he therefore attributes the mixed character of the seed to spontaneous variability. (5/8. ‘Bestimmung des Werthes von Species und Varietat’ 1869 pages 47-72.) But the above distance would be very far from sufficient to prevent intercrossing: cabbages have been known to cross at several times this distance; and the careful Gartner gives many instances of plants growing at from 600 to 800 yards apart fertilising one another. (5/9. ‘Kenntnis der Befruchtung’ 1844 pages 573, 577.) Professor Hoffman even maintains that the flowers of the kidney-bean are specially adapted for self-fertilisation. He enclosed several flowers in bags; and as the buds often dropped off, he attributes the partial sterility of these flowers to the injurious effects of the bags, and not to the exclusion of insects. But the only safe method of experimenting is to cover up a whole plant, which then never suffers.

Self-fertilised seeds were obtained by moving up and down in the same manner as bees do the wing-petals of flowers protected by a net; and crossed seeds were obtained by crossing two of the plants under the same net. The seeds after germinating on sand were planted on the opposite sides of two large pots, and equal-sized sticks were given them to twine up. When 8 inches in height, the plants on the two sides were equal. The crossed plants flowered before the self-fertilised in both pots. As soon as one of each pair had grown to the summit of its stick both were measured.

TABLE 5/53. Phaseolus multiflorus.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 87 : 84 6/8. Pot 1 : 88 : 87. Pot 1 : 82 4/8 : 76.

Pot 2 : 90 : 76 4/8. Pot 2 : 82 4/8 : 87 4/8.

Total : 430.00 : 411.75.

The average height of the five crossed plants is 86 inches, and that of the five self-fertilised plants 82.35; or as 100 to 96. The pots were kept in the greenhouse, and there was little or no difference in the fertility of the two lots. Therefore as far as these few observations serve, the advantage gained by a cross is very small.

Phaseolus vulgaris.

With respect to this species, I merely ascertained that the flowers were highly fertile when insects were excluded, as indeed must be the case, for the plants are often forced during the winter when no insects are present. Some plants of two varieties (namely Canterbury and Fulmer’s Forcing Bean) were covered with a net, and they seemed to produce as many pods, containing as many beans, as some uncovered plants growing alongside; but neither the pods nor the beans were actually counted. This difference in self-fertility between Phaseolus vulgaris and multifloris is remarkable, as these two species are so closely related that Linnaeus thought that they formed one. When the varieties of Phaseolus vulgaris grow near one another in the open ground, they sometimes cross largely, notwithstanding their capacity for self-fertilisation. Mr. Coe has given me a remarkable instance of this fact with respect to the negro and a white-seeded and a brown-seeded variety, which were all grown together. The diversity of character in the seedlings of the second generation raised by me from his plants was wonderful. I could add other analogous cases, and the fact is well-known to gardeners. (5/10. I have given Mr. Coe’s case in the ‘Gardeners’ Chronicle’ 1858 page 829. See also for another case ibid page 845.)

Lathyrus odoratus.

Almost everyone who has studied the structure of papilionaceous flowers has been convinced that they are specially adapted for cross-fertilisation, although many of the species are likewise capable of self-fertilisation. The case therefore of Lathyrus odoratus or the sweet-pea is curious, for in this country it seems invariably to fertilise itself. I conclude that this is so, as five varieties, differing greatly in the colour of their flowers but in no other respect, are commonly sold and come true; yet on inquiry from two great raisers of seed for sale, I find that they take no precautions to insure purity—the five varieties being habitually grown close together. (5/11. See Mr. W. Earley in ‘Nature’ 1872 page 242, to the same effect. He once, however, saw bees visiting the flowers, and supposed that on this occasion they would have been intercrossed.) I have myself purposely made similar trials with the same result. Although the varieties always come true, yet, as we shall presently see, one of the five well-known varieties occasionally gives birth to another, which exhibits all its usual characters. Owing to this curious fact, and to the darker-coloured varieties being the most productive, these increase, to the exclusion of the others, as I was informed by the late Mr. Masters, if there be no selection.

In order to ascertain what would be the effect of crossing two varieties, some flowers on the Purple sweet-pea, which has a dark reddish-purple standard-petal with violet-coloured wing-petals and keel, were castrated whilst very young, and were fertilised with pollen of the Painted Lady. This latter variety has a pale cherry-coloured standard, with almost white wings and keel. On two occasions I raised from a flower thus crossed plants perfectly resembling both parent-forms; but the greater number resembled the paternal variety. So perfect was the resemblance, that I should have suspected some mistake in the label, had not the plants, which were at first identical in appearance with the father or Painted Lady, later in the season produced flowers blotched and streaked with dark purple. This is an interesting example of partial reversion in the same individual plant as it grows older. The purple-flowered plants were thrown away, as they might possibly have been the product of the accidental self-fertilisation of the mother-plant, owing to the castration not having been effectual. But the plants which resembled in the colour of their flowers the paternal variety or Painted Lady were preserved, and their seeds saved. Next summer many plants were raised from these seeds, and they generally resembled their grandfather the Painted Lady, but most of them had their wing-petals streaked and stained with dark pink; and a few had pale purple wings with the standard of a darker crimson than is natural to the Painted Lady, so that they formed a new sub-variety. Amongst these plants a single one appeared having purple flowers like those of the grandmother, but with the petals slightly streaked with a paler tint: this was thrown away. Seeds were again saved from the foregoing plants, and the seedlings thus raised still resembled the Painted Lady, or great-grandfather; but they now varied much, the standard petal varying from pale to dark red, in a few instances with blotches of white; and the wing-petals varied from nearly white to purple, the keel being in all nearly white.

As no variability of this kind can be detected in plants raised from seeds, the parents of which have grown during many successive generations in close proximity, we may infer that they cannot have intercrossed. What does occasionally occur is that in a row of plants raised from seeds of one variety, another variety true of its kind appears; for instance, in a long row of Scarlets (the seeds of which had been carefully gathered from Scarlets for the sake of this experiment) two Purples and one Painted Lady appeared. Seeds from these three aberrant plants were saved and sown in separate beds. The seedlings from both the Purples were chiefly Purples, but with some Painted Ladies and some Scarlets. The seedlings from the aberrant Painted Lady were chiefly Painted Ladies with some Scarlets. Each variety, whatever its parentage may have been, retained all its characters perfect, and there was no streaking or blotching of the colours, as in the foregoing plants of crossed origin. Another variety, however, is often sold, which is striped and blotched with dark purple; and this is probably of crossed origin, for I found, as well as Mr. Masters, that it did not transmit its characters at all truly.

From the evidence now given, we may conclude that the varieties of the sweet-pea rarely or never intercross in this country; and this is a highly remarkable fact, considering, firstly, the general structure of the flowers; secondly, the large quantity of pollen produced, far more than is requisite for self-fertilisation; and thirdly, the occasional visit of insects. That insects should sometimes fail to cross-fertilise the flowers is intelligible, for I have thrice seen humble-bees of two kinds, as well as hive-bees, sucking the nectar, and they did not depress the keel-petals so as to expose the anthers and stigma; they were therefore quite inefficient for fertilising the flowers. One of these bees, namely, Bombus lapidarius, stood on one side at the base of the standard and inserted its proboscis beneath the single separate stamen, as I afterwards ascertained by opening the flower and finding this stamen prised up. Bees are forced to act in this manner from the slit in the staminal tube being closely covered by the broad membranous margin of the single stamen, and from the tube not being perforated by nectar-passages. On the other hand, in the three British species of Lathyrus which I have examined, and in the allied genus Vicia, two nectar-passages are present. Therefore British bees might well be puzzled how to act in the case of the sweet-pea. I may add that the staminal tube of another exotic species, Lathyrus grandiflorus, is not perforated by nectar-passages, and this species has rarely set any pods in my garden, unless the wing-petals were moved up and down, in the same manner as bees ought to do; and then pods were generally formed, but from some cause often dropped off afterwards. One of my sons caught an elephant sphinx-moth whilst visiting the flowers of the sweet-pea, but this insect would not depress the wing-petals and keel. On the other hand, I have seen on one occasion hive-bees, and two or three occasions the Megachile willughbiella in the act of depressing the keel; and these bees had the under sides of their bodies thickly covered with pollen, and could not thus fail to carry pollen from one flower to the stigma of another. Why then do not the varieties occasionally intercross, though this would not often happen, as insects so rarely act in an efficient manner? The fact cannot, as it appears, be explained by the flowers being self-fertilised at a very early age; for although nectar is sometimes secreted and pollen adheres to the viscid stigma before the flowers are fully expanded, yet in five young flowers which were examined by me the pollen-tubes were not exserted. Whatever the cause may be, we may conclude, that in England the varieties never or very rarely intercross. But it does not follow from this, that they would not be cross by the aid of other and larger insects in their native country, which in botanical works is said to be the south of Europe and the East Indies. Accordingly I wrote to Professor Delpino, in Florence, and he informs me “that it is the fixed opinion of gardeners there that the varieties do intercross, and that they cannot be preserved pure unless they are sown separately.”

It follows also from the foregoing facts that the several varieties of the sweet-pea must have propagated themselves in England by self-fertilisation for very many generations, since the time when each new variety first appeared. From the analogy of the plants of Mimulus and Ipomoea, which had been self-fertilised for several generations, and from trials previously made with the common pea, which is in nearly the same state as the sweet-pea, it appeared to me very improbable that a cross between the individuals of the same variety would benefit the offspring. A cross of this kind was therefore not tried, which I now regret. But some flowers of the Painted Lady, castrated at an early age, were fertilised with pollen from the Purple sweet-pea; and it should be remembered that these varieties differ in nothing except in the colour of their flowers. The cross was manifestly effectual (though only two seeds were obtained), as was shown by the two seedlings, when they flowered, closely resembling their father, the Purple pea, excepting that they were a little lighter coloured, with their keels slightly streaked with pale purple. Seeds from flowers spontaneously self-fertilised under a net were at the same time saved from the same mother-plant, the Painted Lady. These seeds unfortunately did not germinate on sand at the same time with the crossed seeds, so that they could not be planted simultaneously. One of the two crossed seeds in a state of germination was planted in a pot (Number 1) in which a self-fertilised seed in the same state had been planted four days before, so that this latter seedling had a great advantage over the crossed one. In Pot 2 the other crossed seed was planted two days before a self-fertilised one; so that here the crossed seedling had a considerable advantage over the self-fertilised one. But this crossed seedling had its summit gnawed off by a slug, and was in consequence for a time quite beaten by the self-fertilised plant. Nevertheless I allowed it to remain, and so great was its constitutional vigour that it ultimately beat its uninjured self-fertilised rival. When all four plants were almost fully grown they were measured, as here shown:—

TABLE 5/54. Lathyrus odoratus.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 80 : 64 4/8.

Pot 2 : 78 4/8 : 63.

Total : 158.5 : 127.5.

The two crossed plants here average 79.25, and the two self-fertilised 63.75 inches in height, or as 100 to 80. Six flowers on these two crossed plants were reciprocally crossed with pollen from the other plant, and the six pods thus produced contained on an average six peas, with a maximum in one of seven. Eighteen spontaneously self-fertilised pods from the Painted Lady, which, as already stated, had no doubt been self-fertilised for many previous generations, contained on an average only 3.93 peas, with a maximum in one of five peas; so that the number of peas in the crossed and self-fertilised pods was as 100 to 65. The self-fertilised peas were, however, quite as heavy as those from the crossed pods. From these two lots of seeds, the plants of the next generation were raised.

PLANTS OF THE SECOND GENERATION.

Many of the self-fertilised peas just referred to germinated on sand before any of the crossed ones, and were rejected. As soon as I got equal pairs, they were planted on the opposite sides of two large pots, which were kept in the greenhouse. The seedlings thus raised were the grandchildren of the Painted Lady, which was first crossed by the Purple variety. When the two lots were from 4 to 6 inches in height there was no difference between them. Nor was there any marked difference in the period of their flowering. When fully grown they were measured, as follows:—

TABLE 5/55. Lathyrus odoratus (Second Generation).

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Seedlings from Plants Crossed during the two previous Generations.

Column 3: Seedlings from Plants Self-fertilised during many previous Generations.

Pot 1 : 72 4/8 : 57 4/8. Pot 1 : 71 : 67. Pot 1 : 52 2/8 : 56 2/8.

Pot 2 : 81 4/8 : 66 2/8. Pot 2 : 45 2/8 : 38 7/8. Pot 2 : 55 : 46.

Total : 377.50 : 331.86.

The average height of the six crossed plants is here 62.91, and that of the six self-fertilised 55.31 inches; or as 100 to 88. There was not much difference in the fertility of the two lots; the crossed plants having produced in the greenhouse thirty-five pods, and the self-fertilised thirty-two pods.

Seeds were saved from the self-fertilised flowers on these two lots of plants, for the sake of ascertaining whether the seedlings thus raised would inherit any difference in growth or vigour. It must therefore be understood that both lots in the following trial are plants of self-fertilised parentage; but that in the one lot the plants were the children of plants which had been crossed during two previous generations, having been before that self-fertilised for many generations; and that in the other lot they were the children of plants which had not been crossed for very many previous generations. The seeds germinated on sand and were planted in pairs on the opposite sides of four pots. They were measured, when fully grown, with the following result:—

TABLE 5/56. Lathyrus odoratus.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Self-fertilised Plants from Crossed Plants.

Column 3: Self-fertilised Plants from Self-fertilised Plants.

Pot 1 : 72 : 65. Pot 1 : 72 : 61 4/8.

Pot 2 : 58 : 64. Pot 2 : 68 : 68 2/8. Pot 2 : 72 4/8 : 56 4/8.

Pot 3 : 81 : 60 2/8.

Pot 4 : 77 4/8 : 76 4/8.

Total : 501 : 452.

The average height of the seven self-fertilised plants, the offspring of crossed plants, is 71.57, and that of the seven self-fertilised plants, the offspring of self-fertilised plants, is 64.57; or as 100 to 90. The self-fertilised plants from the self-fertilised produced rather more pods—namely, thirty-six—than the self-fertilised plants from the crossed, for these produced only thirty-one pods.

A few seeds of the same two lots were sown in the opposite corners of a large box in which a Brugmansia had long been growing, and in which the soil was so exhausted that seeds of Ipomoea purpurea would hardly vegetate; yet the two plants of the sweet-pea which were raised flourished well. For a long time the self-fertilised plant from the self-fertilised beat the self-fertilised plant from the crossed plant; the former flowered first, and was at one time 77 1/2 inches, whilst the latter was only 68 1/2 in height; but ultimately the plant from the previous cross showed its superiority and attained a height of 108 1/2 inches, whilst the other was only 95 inches. I also sowed some of the same two lots of seeds in poor soil in a shady place in a shrubbery. Here again the self-fertilised plants from the self-fertilised for a long time exceeded considerably in height those from the previously crossed plants; and this may probably be attributed, in the present as in the last case, to these seeds having germinated rather sooner than those from the crossed plants; but at the close of the season the tallest of the self-fertilised plants from the crossed plants was 30 inches, whilst the tallest of the self-fertilised from the self-fertilised was 29 3/8 inches in height.

From the various facts now given we see that plants derived from a cross between two varieties of the sweet-pea, which differ in no respect except in the colour of their flowers, exceed considerably in height the offspring from self-fertilised plants, both in the first and second generations. The crossed plants also transmit their superiority in height and vigour to their self-fertilised offspring.

Pisum sativum.

The common pea is perfectly fertile when its flowers are protected from the visits of insects; I ascertained this with two or three different varieties, as did Dr. Ogle with another. But the flowers are likewise adapted for cross-fertilisation; Mr. Farrer specifies the following points, namely: “The open blossom displaying itself in the most attractive and convenient position for insects; the conspicuous vexillum; the wings forming an alighting place; the attachment of the wings to the keel, by which any body pressing on the former must press down the latter; the staminal tube enclosing nectar, and affording by means of its partially free stamen with apertures on each side of its base an open passage to an insect seeking the nectar; the moist and sticky pollen placed just where it will be swept out of the apex of the keel against the entering insect; the stiff elastic style so placed that on a pressure being applied to the keel it will be pushed upwards out of the keel; the hairs on the style placed on that side of the style only on which there is space for the pollen, and in such a direction as to sweep it out; and the stigma so placed as to meet an entering insect,—all these become correlated parts of one elaborate mechanism, if we suppose that the fertilisation of these flowers is effected by the carriage of pollen from one to the other.” (5/12. ‘Nature’ October 10, 1872 page 479. Hermann Muller gives an elaborate description of the flowers ‘Befruchtung’ etc. page 247.) Notwithstanding these manifest provisions for cross-fertilisation, varieties which have been cultivated for very many successive generations in close proximity, although flowering at the same time, remain pure. I have elsewhere given evidence on this head, and if required could give more. (5/13. ‘Variation of Animals and Plants under Domestication’ chapter 9 2nd edition volume 1 page 348.) There can hardly be a doubt that some of Knight’s varieties, which were originally produced by an artificial cross and were very vigorous, lasted for at least sixty years, and during all these years were self-fertilised; for had it been otherwise, they would not have kept true, as the several varieties are generally grown near together. Most of the varieties, however, endure for a shorter period; and this may be in part due to their weakness of constitution from long-continued self-fertilisation.

It is remarkable, considering that the flowers secrete much nectar and afford much pollen, how seldom they are visited by insects either in England, or, as H. Muller remarks, in North Germany. I have observed the flowers for the last thirty years, and in all this time have only thrice seen bees of the proper kind at work (one of them being Bombus muscorum), such as were sufficiently powerful to depress the keel, so as to get the undersides of their bodies dusted with pollen. These bees visited several flowers, and could hardly have failed to cross-fertilise them. Hive-bees and other small kinds sometimes collect pollen from old and already fertilised flowers, but this is of no account. The rarity of the visits of efficient bees to this exotic plant is, I believe, the chief cause of the varieties so seldom intercrossing. That a cross does occasionally take place, as might be expected from what has just been stated, is certain, from the recorded cases of the direct action of the pollen of one variety on the seed-coats of another. (5/14. ‘Variation of Animals and Plants under Domestication’ chapter 11 2nd edition volume 1 page 428.) The late Mr. Masters, who particularly attended to the raising of new varieties of peas, was convinced that some of them had originated from accidental crosses. But as such crosses are rare, the old varieties would not often be thus deteriorated, more especially as plants departing from the proper type are generally rejected by those who collect seed for sale. There is another cause which probably tends to render cross-fertilisation rare, namely, the early age at which the pollen-tubes are exserted; eight flowers not fully expanded were examined, and in seven of these the pollen-tubes were in this state; but they had not as yet penetrated the stigma. Although so few insects visit the flowers of the pea in this country or in North Germany, and although the anthers seem here to open abnormally soon, it does not follow that the species in its native country would be thus circumstanced.

Owing to the varieties having been self-fertilised for many generations, and to their having been subjected in each generation to nearly the same conditions (as will be explained in a future chapter) I did not expect that a cross between two such plants would benefit the offspring; and so it proved on trial. In 1867 I covered up several plants of the Early Emperor pea, which was not then a very new variety, so that it must already have been propagated by self-fertilisation for at least a dozen generations. Some flowers were crossed with pollen from a distinct plant growing in the same row, and others were allowed to fertilise themselves under a net. The two lots of seeds thus obtained were sown on opposite sides of two large pots, but only four pairs came up at the same time. The pots were kept in the greenhouse. The seedlings of both lots when between 6 and 7 inches in height were equal. When nearly full-grown they were measured, as in Table 5/57.

TABLE 5/57. Pisum sativum.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 35 : 29 6/8.

Pot 2 : 31 4/8 : 51. Pot 2 : 35 : 45. Pot 2 : 37 : 33.

Total : 138.50 : 158.75.

The average height of the four crossed plants is here 34.62, and that of the four self-fertilised plants 39.68, or as 100 to 115. So that the crossed plants, far from beating the self-fertilised, were completely beaten by them.

There can be no doubt that the result would have been widely different, if any two varieties out of the numberless ones which exist had been crossed. Notwithstanding that both had been self-fertilised for many previous generations, each would almost certainly have possessed its own peculiar constitution; and this degree of differentiation would have been sufficient to make a cross highly beneficial. I have spoken thus confidently of the benefit which would have been derived from crossing any two varieties of the pea from the following facts: Andrew Knight in speaking of the results of crossing reciprocally very tall and short varieties, says, “I had in this experiment a striking instance of the stimulative effects of crossing the breeds; for the smallest variety, whose height rarely exceeded 2 feet, was increased to 6 feet; whilst the height of the large and luxuriant kind was very little diminished.” (5/15. ‘Philosophical Transactions’ 1799 page 200.) Recently Mr. Laxton has made numerous crosses, and everyone had been astonished at the vigour and luxuriance of the new varieties which he has thus raised and afterwards fixed by selection. He gave me seed-peas produced from crosses between four distinct kinds; and the plants thus raised were extraordinarily vigorous, being in each case from 1 to 2 or even 3 feet taller than the parent-forms, which were raised at the same time close alongside. But as I did not measure their actual height I cannot give the exact ratio, but it must have been at least as 100 to 75. A similar trial was subsequently made with two other peas from a different cross, and the result was nearly the same. For instance, a crossed seedling between the Maple and Purple-podded pea was planted in poor soil and grew to the extraordinary height of 116 inches; whereas the tallest plant of either parent variety, namely, a Purple-podded pea, was only 70 inches in height; or as 100 to 60.

Sarothamnus scoparius.

Bees incessantly visit the flowers of the common Broom, and these are adapted by a curious mechanism for cross-fertilisation. When a bee alights on the wing-petals of a young flower, the keel is slightly opened and the short stamens spring out, which rub their pollen against the abdomen of the bee. If a rather older flower is visited for the first time (or if the bee exerts great force on a younger flower), the keel opens along its whole length, and the longer as well as the shorter stamens, together with the much elongated curved pistil, spring forth with violence. The flattened, spoon-like extremity of the pistil rests for a time on the back of the bee, and leaves on it the load of pollen with which it is charged. As soon as the bee flies away, the pistil instantly curls round, so that the stigmatic surface is now upturned and occupies a position, in which it would be rubbed against the abdomen of another bee visiting the same flower. Thus, when the pistil first escapes from the keel, the stigma is rubbed against the back of the bee, dusted with pollen from the longer stamens, either of the same or another flower; and afterwards against the lower surface of the bee dusted with pollen from the shorter stamens, which is often shed a day or two before that from the longer stamens. (5/16. These observations have been quoted in an abbreviated form by the Reverend G. Henslow, in the ‘Journal of Linnean Society Botany’ volume 9 1866 page 358. Hermann Muller has since published a full and excellent account of the flower in his ‘Befruchtung’ etc. page 240.) By this mechanism cross-fertilisation is rendered almost inevitable, and we shall immediately see that pollen from a distinct plant is more effective than that from the same flower. I need only add that, according to H. Muller, the flowers do not secrete nectar, and he thinks that bees insert their proboscides only in the hope of finding nectar; but they act in this manner so frequently and for so long a time that I cannot avoid the belief that they obtain something palatable within the flowers.

If the visits of bees are prevented, and if the flowers are not dashed by the wind against any object, the keel never opens, so that the stamens and pistil remain enclosed. Plants thus protected yield very few pods in comparison with those produced by neighbouring uncovered bushes, and sometimes none at all. I fertilised a few flowers on a plant growing almost in a state of nature with pollen from another plant close alongside, and the four crossed capsules contained on an average 9.2 seeds. This large number no doubt was due to the bush being covered up, and thus not exhausted by producing many pods; for fifty pods gathered from an adjoining plant, the flowers of which had been fertilised by the bees, contained an average of only 7.14 seeds. Ninety-three pods spontaneously self-fertilised on a large bush which had been covered up, but had been much agitated by the wind, contained an average of 2.93 seeds. Ten of the finest of these ninety-three capsules yielded an average of 4.30 seeds, that is less than half the average number in the four artificially crossed capsules. The ratio of 7.14 to 2.93, or as 100 to 41, is probably the fairest for the number of seeds per pod, yielded by naturally-crossed and spontaneously self-fertilised flowers. The crossed seeds compared with an equal number of the spontaneously self-fertilised seeds were heavier, in the ratio of 100 to 88. We thus see that besides the mechanical adaptations for cross-fertilisation, the flowers are much more productive with pollen from a distinct plant than with their own pollen.

Eight pairs of the above crossed and self-fertilised seeds, after they had germinated on sand, were planted (1867) on the opposite sides of two large pots. When several of the seedlings were an inch and a half in height, there was no marked difference between the two lots. But even at this early age the leaves of the self-fertilised seedlings were smaller and of not so bright a green as those of the crossed seedlings. The pots were kept in the greenhouse, and as the plants on the following spring (1868) looked unhealthy and had grown but little, they were plunged, still in their pots, into the open ground. The plants all suffered much from the sudden change, especially the self-fertilised, and two of the latter died. The remainder were measured, and I give the measurements in Table 5/58, because I have not seen in any other species so great a difference between the crossed and self-fertilised seedlings at so early an age.

TABLE 5/58. Sarothamnus scoparius (very young plants).

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 4 4/8 : 2 4/8. Pot 1 : 6 : 1 4/8. Pot 1 : 2 : 1.

Pot 2 : 2 : 1 4/8. Pot 2 : 2 4/8 : 1. Pot 2 : 0 4/8 : 0 4/8.

Total : 17.5 : 8.0.

The six crossed plants here average 2.91, and the six self-fertilised 1.33 inches in height; so that the former were more than twice as high as the latter, or as 100 to 46.

In the spring of the succeeding year (1869) the three crossed plants in Pot 1 had all grown to nearly a foot in height, and they had smothered the three little self-fertilised plants so completely that two were dead; and the third, only an inch and a half in height, was dying. It should be remembered that these plants had been bedded out in their pots, so that they were subjected to very severe competition. This pot was now thrown away.

The six plants in Pot 2 were all alive. One of the self-fertilised was an inch and a quarter taller than any one of the crossed plants; but the other two self-fertilised plants were in a very poor condition. I therefore resolved to leave these plants to struggle together for some years. By the autumn of the same year (1869) the self-fertilised plant which had been victorious was now beaten. The measurements are shown in Table 5/59.

TABLE 5/59. Pot 2.—Sarothamnus scoparius.

Heights of plants measured in inches.

Column 1: Crossed Plants.

Column 2: Self-fertilised Plants.

The same plants were again measured in the autumn of the following year, 1870.

TABLE 5/60. Pot 2.—Sarothamnus scoparius.

Heights of plants measured in inches.

Column 1: Crossed Plants.

Column 2: Self-fertilised Plants.

Total : 56.75 : 35.50.

The three crossed plants now averaged 18.91, and the three self-fertilised 11.83 inches in height; or as 100 to 63. The three crossed plants in Pot 1, as already shown, had beaten the three self-fertilised plants so completely, that any comparison between them was superfluous.

The winter of 1870-1871 was severe. In the spring the three crossed plants in Pot 2 had not even the tips of their shoots in the least injured, whereas all three self-fertilised plants were killed half-way down to the ground; and this shows how much more tender they were. In consequence not one of these latter plants bore a single flower during the ensuing summer of 1871, whilst all three crossed plants flowered.

Ononis minutissima.

This plant, of which seeds were sent me from North Italy, produces, besides the ordinary papilionaceous flowers, minute, imperfect, closed or cleistogene flowers, which can never be cross-fertilised, but are highly self-fertile. Some of the perfect flowers were crossed with pollen from a distinct plant, and six capsules thus produced yielded on an average 3.66 seeds, with a maximum of five in one. Twelve perfect flowers were marked and allowed to fertilise themselves spontaneously under a net, and they yielded eight capsules, containing on an average 2.38 seeds, with a maximum of three seeds in one. So that the crossed and self-fertilised capsules from the perfect flowers yielded seeds in the proportion of 100 to 65. Fifty-three capsules produced by the cleistogene flowers contained on an average 4.1 seeds, so that these were the most productive of all; and the seeds themselves looked finer even than those from the crossed perfect flowers.

The seeds from the crossed perfect flowers and from the self-fertilised cleistogene flowers were allowed to germinate on sand; but unfortunately only two pairs germinated at the same time. These were planted on the opposite sides of the same pot, which was kept in the greenhouse. In the summer of the same year, when the seedlings were about 4 1/2 inches in height, the two lots were equal. In the autumn of the following year (1868) the two crossed plants were of exactly the same height, namely, 11 4/8 inches, and the two self-fertilised plants 12 6/8 and 7 2/8 inches; so that one of the self-fertilised exceeded considerably in height all the others. By the autumn of 1869 the two crossed plants had acquired the supremacy; their height being 16 4/8 and 15 1/8, whilst that of the two self-fertilised plants was 14 5/8 and 11 4/8 inches.

By the autumn of 1870, the heights were as follows:—

TABLE 5/61. Ononis minutissima.

Heights of plants measured in inches.

Column 1: Crossed Plants.

Column 2: Self-fertilised Plants.

Total : 39.63 : 34.75.

So that the mean height of the two crossed plants was 19.81, and that of the two self-fertilised 17.37 inches; or as 100 to 88. It should be remembered that the two lots were at first equal in height; that one of the self-fertilised plants then had the advantage, the two crossed plants being at last victorious.]

A SUMMARY ON THE LEGUMINOSAE.

Six genera in this family were experimented on, and the results are in some respects remarkable. The crossed plants of the two species of Lupinus were conspicuously superior to the self-fertilised plants in height and fertility; and when grown under very unfavourable conditions, in vigour. The scarlet-runner (Phaseolus multiflorus) is partially sterile if the visits of bees are prevented, and there is reason to believe that varieties growing near one another intercross. The five crossed plants, however, exceeded in height the five self-fertilised only by a little. Phaseolus vulgaris is perfectly self-sterile; nevertheless, varieties growing in the same garden sometimes intercross largely. The varieties of Lathyrus odoratus, on the other hand, appear never to intercross in this country; and though the flowers are not often visited by efficient insects, I cannot account for this fact, more especially as the varieties are believed to intercross in North Italy. Plants raised from a cross between two varieties, differing only in the colour of their flowers, grew much taller and were under unfavourable conditions more vigorous than the self-fertilised plants; they also transmitted, when self-fertilised, their superiority to their offspring. The many varieties of the common Pea (Pisum sativum), though growing in close proximity, very seldom intercross; and this seems due to the rarity in this country of the visits of bees sufficiently powerful to effect cross-fertilisation. A cross between the self-fertilised individuals of the same variety does no good whatever to the offspring; whilst a cross between distinct varieties, though closely allied, does great good, of which we have excellent evidence. The flowers of the Broom (Sarothamnus) are almost sterile if they are not disturbed and if insects are excluded. The pollen from a distinct plant is more effective than that from the same flower in producing seeds. The crossed seedlings have an enormous advantage over the self-fertilised when grown together in close competition. Lastly, only four plants of the Ononis minutissima were raised; but as these were observed during their whole growth, the advantage of the crossed over the self-fertilised plants may, I think, be fully trusted.

[15. ONAGRACEAE.—Clarkia elegans.

Owing to the season being very unfavourable (1867), few of the flowers which I fertilised formed capsules; twelve crossed flowers produced only four, and eighteen self-fertilised flowers yielded only one capsule. The seeds after germinating on sand were planted in three pots, but all the self-fertilised plants died in one of them. When the two lots were between 4 and 5 inches in height, the crossed began to show a slight superiority over the self-fertilised. When in full flower they were measured, with the following result:—

TABLE 5/62. Clarkia elegans.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 40 4/8 : 33. Pot 1 : 35 : 24. Pot 1 : 25 : 23.

Pot 2 : 33 4/8 : 30 4/8.

Total : 134.0 : 110.5.

The average height of the four crossed plants is 33.5, and that of the four self-fertilised plants 27.62 inches, or as 100 to 82. The crossed plants altogether produced 105 and the self-fertilised plants 63 capsules; or as 100 to 60. In both pots a self-fertilised plant flowered before any one of the crossed plants.

16. LOASACEAE.—Bartonia aurea.

Some flowers were crossed and self-fertilised in the usual manner during two seasons; but as I reared on the first occasion only two pairs, the results are given together. On both occasions the crossed capsules contained slightly more seeds than the self-fertilised. During the first year, when the plants were about 7 inches in height, the self-fertilised were the tallest, and in the second year the crossed were the tallest. When the two lots were in full flower they were measured, as in Table 5/63.

TABLE 5/63. Bartonia aurea.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 31 : 37.

Pot 2 : 18 4/8 : 20 4/8.

Pot 3 : 19 4/8 : 40 4/8.

Pot 4 : 25 : 35. Pot 4 : 36 : 15 4/8.

Pot 5 : 31 : 18. Pot 5 : 16 : 11 4/8.

Pot 6 : 20 : 32 4/8.

Total : 197.0 : 210.5.

The average height of the eight crossed plants is 24.62, and that of the eight self-fertilised 26.31 inches; or as 100 to 107. So that the self-fertilised had a decided advantage over the crossed. But the plants from some cause never grew well, and finally became so unhealthy that only three crossed and three self-fertilised plants survived to set any capsules, and these were few in number. The two lots seemed to be about equally unproductive.

17. PASSIFLORACEAE.—Passiflora gracilis.

This annual species produces spontaneously numerous fruits when insects are excluded, and behaves in this respect very differently from most of the other species in the genus, which are extremely sterile unless fertilised with pollen from a distinct plant. (5/17. ‘Variation of Animals and Plants under Domestication’ chapter 17 2nd edition volume 2 page 118.) Fourteen fruits from crossed flowers contained on an average 24.14 seeds. Fourteen fruits (two poor ones being rejected), spontaneously self-fertilised under a net, contained on an average 20.58 seeds per fruit; or as 100 to 85. These seeds were sown on the opposite sides of three pots, but only two pairs came up at the same time; and therefore a fair judgment cannot be formed.

TABLE 5/64. Passiflora gracilis.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 56 : 38.

Pot 2 : 42 : 64.

Total : 98 : 102.

The mean of the two crossed is 49 inches, and that of the two self-fertilised 51 inches; or as 100 to 104.

18. UMBELLIFERAE.—Apium petroselinum.

The Umbelliferae are proterandrous, and can hardly fail to be cross-fertilised by the many flies and small Hymenoptera which visit the flowers. (5/18. Hermann Muller ‘Befruchtung’ etc. page 96. According to M. Mustel as stated by Godron ‘De l’espèce’ tome 2 page 58 1859, varieties of the carrot growing near each other readily intercross.) A plant of the common parsley was covered by a net, and it apparently produced as many and as fine spontaneously self-fertilised fruits or seeds as the adjoining uncovered plants. The flowers on the latter were visited by so many insects that they must have received pollen from one another. Some of these two lots of seeds were left on sand, but nearly all the self-fertilised seeds germinated before the others, so that I was forced to throw all away. The remaining seeds were then sown on the opposite sides of four pots. At first the self-fertilised seedlings were a little taller in most of the pots than the naturally crossed seedlings, and this no doubt was due to the self-fertilised seeds having germinated first. But in the autumn all the plants were so equal that it did not seem worth while to measure them. In two of the pots they were absolutely equal; in a third, if there was any difference, it was in favour of the crossed plants, and in a somewhat plainer manner in the fourth pot. But neither side had any substantial advantage over the other; so that in height they may be said to be as 100 to 100.

19. DIPSACEAE.—Scabiosa atro-purpurea.

The flowers, which are proterandrous, were fertilised during the unfavourable season of 1867, so that I got few seeds, especially from the self-fertilised heads, which were extremely sterile. The crossed and self-fertilised plants raised from these seeds were measured before they were in full flower, as in Table 5/65.

TABLE 5/65. Scabiosa atro-purpurea.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 14 : 20.

Pot 2 : 15 : 14 4/8.

Pot 3 : 21 : 14. Pot 3 : 18 4/8 : 13.

Total : 68.5 : 61.5.

The four crossed plants averaged 17.12, and the four self-fertilised 15.37 inches in height; or as 100 to 90. One of the self-fertilised plants in Pot 3 was killed by an accident, and its fellow pulled up; so that when they were again measured to the summits of their flowers, there were only three on each side; the crossed now averaged in height 32.83, and the self-fertilised 30.16 inches; or as 100 to 92.

20. COMPOSITAE.—Lactuca sativa. (5/19. The Compositae are well-adapted for cross-fertilisation, but a nurseryman on whom I can rely, told me that he had been in the habit of sowing several kinds of lettuce near together for the sake of seed, and had never observed that they became crossed. It is very improbable that all the varieties which were thus cultivated near together flowered at different times; but two which I selected by hazard and sowed near each other did not flower at the same time; and my trial failed.)

Three plants of Lettuce (Great London Cos var.) grew close together in my garden; one was covered by a net, and produced self-fertilised seeds, the other two were allowed to be naturally crossed by insects; but the season (1867) was unfavourable, and I did not obtain many seeds. Only one crossed and one self-fertilised plant were raised in Pot 1, and their measurements are given in Table 5/66. The flowers on this one self-fertilised plant were again self-fertilised under a net, not with pollen from the same floret, but from other florets on the same head. The flowers on the two crossed plants were left to be crossed by insects, but the process was aided by some pollen being occasionally transported by me from plant to plant. These two lots of seeds, after germinating on sand, were planted in pairs on the opposite sides of Pots 2 and 3, which were at first kept in the greenhouse and then turned out of doors. The plants were measured when in full flower. Table 5/66, therefore, includes plants belonging to two generations. When the seedlings of the two lots were only 5 or 6 inches in height they were equal. In Pot 3 one of the self-fertilised plants died before flowering, as has occurred in so many other cases.

TABLE 5/66. Lactuca sativa.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 27 : 21 4/8. Pot 1 : 25 : 20. First generation, planted in open ground.

Pot 2 : 29 4/8 : 24. Pot 2 : 17 4/8 : 10. Pot 2 : 12 4/8 : 11. Second generation, planted in open ground.

Pot 3 : 14 : 9 4/8. Pot 3 : 10 4/8 : 0. Second generation, kept in the pot.

Total : 136 : 96.

The average height of the seven crossed plants is 19.43, and that of the six self-fertilised plants 16 inches; or as 100 to 82.

21. CAMPANULACEAE.—Specularia speculum.

In the closely allied genus, Campanula, in which Specularia was formerly included, the anthers shed at an early period their pollen, and this adheres to the collecting hairs which surround the pistil beneath the stigma; so that without some mechanical aid the flowers cannot be fertilised. For instance, I covered up a plant of Campanula carpathica, and it did not produce a single capsule, whilst the surrounding uncovered plants seeded profusely. On the other hand, the present species of Specularia appears to set almost as many capsules when covered up, as when left to the visits of the Diptera, which, as far as I have seen, are the only insects that frequent the flowers. (5/20. It has long been known that another species of the genus, Specularia perfoliata, produces cleistogene as well as perfect flowers, and the former are of course self-fertile.) I did not ascertain whether the naturally crossed and spontaneously self-fertilised capsules contained an equal number of seeds, but a comparison of artificially crossed and self-fertilised flowers, showed that the former were probably the most productive. It appears that this plant is capable of producing a large number of self-fertilised capsules owing to the petals closing at night, as well as during cold weather. In the act of closing, the margins of the petals become reflexed, and their inwardly projecting midribs then pass between the clefts of the stigma, and in doing so push the pollen from the outside of the pistil on to the stigmatic surfaces. (5/21. Mr. Meehan has lately shown ‘Proceedings of the Academy of Natural Science Philadelphia’ May 16, 1876 page 84, that the closing of the flowers of Claytonia virginica and Ranunculus bulbosus during the night causes their self-fertilisation.)

Twenty flowers were fertilised by me with their own pollen, but owing to the bad season, only six capsules were produced; they contained on an average 21.7 seeds, with a maximum of forty-eight in one. Fourteen flowers were crossed with pollen from another plant, and these produced twelve capsules, containing on an average 30 seeds, with a maximum in one of fifty-seven seeds; so that the crossed seeds were to the self-fertilised from an equal number of capsules as 100 to 72. The former were also heavier than an equal number of self-fertilised seeds, in the ratio of 100 to 86. Thus, whether we judge by the number of capsules produced from an equal number of flowers, or by the average number of the contained seeds, or the maximum number in any one capsule, or by their weight, crossing does great good in comparison with self-fertilisation. The two lots of seeds were sown on the opposite sides of four pots; but the seedlings were not sufficiently thinned. Only the tallest plant on each side was measured, when fully grown. The measurements are given in Table 5/67. In all four pots the crossed plants flowered first. When the seedlings were only about an inch and a half in height both lots were equal.

TABLE 5/67. Specularia speculum.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Tallest Crossed Plant in each Pot.

Column 3: Tallest Self-fertilised Plant in each Pot.

Pot 1 : 18 : 15 6/8.

Pot 2 : 17 : 19.

Pot 3 : 22 1/8 : 18.

Pot 4 : 20 : 23.

Total : 77.13 : 75.75.

The four tallest crossed plants averaged 19.28, and the four tallest self-fertilised 18.93 inches in height; or as 100 to 98. So that there was no difference worth speaking of between the two lots in height; though other great advantages are derived, as we have seen, from cross-fertilisation. From being grown in pots and kept in the greenhouse, none of the plants produced any capsules.

Lobelia ramosa. (5/22. I have adopted the name given to this plant in the ‘Gardeners’ Chronicle’ 1866. Professor T. Dyer, however, informs me that it probably is a white variety of L. tenuior of R. Brown, from W. Australia.)

VAR. SNOW-FLAKE.

The well-adapted means by which cross-fertilisation is ensured in this genus have been described by several authors. (5/23. See the works of Hildebrand and Delpino. Mr. Farrer also has given a remarkably clear description of the mechanism by which cross-fertilisation is effected in this genus, in the ‘Annals and Magazine of Natural History’ volume 2 4th series 1868 page 260. In the allied genus Isotoma, the curious spike which projects rectangularly from the anthers, and which when shaken causes the pollen to fall on the back of an entering insect, seems to have been developed from a bristle, like one of those which spring from the anthers in some of or all the species of Lobelia, as described by Mr. Farrer.) The pistil as it slowly increases in length pushes the pollen out of the conjoined anthers, by the aid of a ring of bristles; the two lobes of the stigma being at this time closed and incapable of fertilisation. The extrusion of the pollen is also aided by insects, which rub against the little bristles that project from the anthers. The pollen thus pushed out is carried by insects to the older flowers, in which the stigma of the now freely projecting pistil is open and ready to be fertilised. I proved the importance of the gaily-coloured corolla, by cutting off the large flowers of Lobelia erinus; and these flowers were neglected by the hive-bees which were incessantly visiting the other flowers.

A capsule was obtained by crossing a flower of L. ramosa with pollen from another plant, and two other capsules from artificially self-fertilised flowers. The contained seeds were sown on the opposite sides of four pots. Some of the crossed seedlings which came up before the others had to be pulled up and thrown away. Whilst the plants were very small there was not much difference in height between the two lots; but in Pot 3 the self-fertilised were for a time the tallest. When in full flower the tallest plant on each side of each pot was measured, and the result is shown in Table 5/68. In all four pots a crossed plant flowered before any one of its opponents.

TABLE 5/68. Lobelia ramosa (First Generation).

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Tallest Crossed Plant in each Pot.

Column 3: Tallest Self-fertilised Plant in each Pot.

Pot 1 : 22 4/8 : 17 4/8.

Pot 2 : 27 4/8 : 24.

Pot 3 : 16 4/8 : 15.

Pot 4 : 22 4/8 : 17.

Total : 89.0 : 73.5.

The four tallest crossed plants averaged 22.25, and the four tallest self-fertilised 18.37 inches in height; or as 100 to 82. I was surprised to find that the anthers of a good many of these self-fertilised plants did not cohere and did not contain any pollen; and the anthers even of a very few of the crossed plants were in the same condition. Some flowers on the crossed plants were again crossed, four capsules being thus obtained; and some flowers on the self-fertilised plants were again self-fertilised, seven capsules being thus obtained. The seeds from both lots were weighed, and it was calculated that an equal number of capsules would have yielded seed in the proportion by weight of 100 for the crossed to 60 for the self-fertilised capsules. So that the flowers on the crossed plants again crossed were much more fertile than those on the self-fertilised plants again self-fertilised.

PLANTS OF THE SECOND GENERATION.

The above two lots of seeds were placed on damp sand, and many of the crossed seeds germinated, as on the last occasion, before the self-fertilised, and were rejected. Three or four pairs in the same state of germination were planted on the opposite sides of two pots; a single pair in a third pot; and all the remaining seeds were sown crowded in a fourth pot. When the seedlings were about one and a half inches in height, they were equal on both sides of the three first pots; but in Pot 4, in which they grew crowded and were thus exposed to severe competition, the crossed were about a third taller than the self-fertilised. In this latter pot, when the crossed averaged 5 inches in height, the self-fertilised were about 4 inches; nor did they look nearly such fine plants. In all four pots the crossed plants flowered some days before the self-fertilised. When in full flower the tallest plant on each side was measured; but before this time the single crossed plant in Pot 3, which was taller than its antagonist, had died and was not measured. So that only the tallest plant on each side of three pots was measured, as in Table 5/69.

TABLE 5/69. Lobelia ramosa (Second Generation).

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Tallest Crossed Plant in each Pot.

Column 3: Tallest Self-fertilised Plant in each Pot.

Pot 1 : 27 4/8 : 18 4/8.

Pot 2 : 21 : 19 4/8.

Pot 3 : 21 4/8 : 19. Crowded.

Total : 70 : 57.

The average height of the three tallest crossed plants is here 23.33, and that of the tallest self-fertilised 19 inches; or as 100 to 81. Besides this difference in height, the crossed plants were much more vigorous and more branched than the self-fertilised plants, and it is unfortunate that they were not weighed.

Lobelia fulgens.

This species offers a somewhat perplexing case. In the first generation the self-fertilised plants, though few in number, greatly exceeded the crossed in height; whilst in the second generation, when the trial was made on a much larger scale, the crossed beat the self-fertilised plants. As this species is generally propagated by off-sets, some seedlings were first raised, in order to have distinct plants. On one of these plants several flowers were fertilised with their own pollen; and as the pollen is mature and shed long before the stigma of the same flower is ready for fertilisation, it was necessary to number each flower and keep its pollen in paper with a corresponding number. By this means well-matured pollen was used for self-fertilisation. Several flowers on the same plant were crossed with pollen from a distinct individual, and to obtain this the conjoined anthers of young flowers were roughly squeezed, and as it is naturally protruded very slowly by the growth of the pistil, it is probable that the pollen used by me was hardly mature, certainly less mature than that employed for self-fertilisation. I did not at the time think of this source of error, but I now suspect that the growth of the crossed plants was thus injured. Anyhow the trial was not perfectly fair. Opposed to the belief that the pollen used in crossing was not in so good a state as that used for self-fertilisation, is the fact that a greater proportional number of the crossed than of the self-fertilised flowers produced capsules; but there was no marked difference in the amount of seed contained in the capsules of the two lots. (5/24. Gartner has shown that certain plants of Lobelia fulgens are quite sterile with pollen from the same plant, though this pollen is efficient on any other individual; but none of the plants on which I experimented, which were kept in the greenhouse, were in this peculiar condition.)

As the seeds obtained by the above two methods would not germinate when left on bare sand, they were sown on the opposite sides of four pots; but I succeeded in raising only a single pair of seedlings of the same age in each pot. The self-fertilised seedlings, when only a few inches in height, were in most of the pots taller than their opponents; and they flowered so much earlier in all the pots, that the height of the flower-stems could be fairly compared only in Pots 1 and 2.

TABLE 5/70. Lobelia fulgens (First Generation).

Heights of flower-stems measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Height of Flower-stems on the Crossed Plants.

Column 3: Height of Flower-stems on the Self-fertilised Plants.

Pot 1 : 33 : 50.

Pot 2 : 36 4/8 : 38 4/8.

Pot 3 : 21* : 43.

Pot 4 : 12* : 35 6/8.

*Not in full flower.

The mean height of the flower-stems of the two crossed plants in Pots 1 and 2 is here 34.75 inches, and that of the two self-fertilised plants in the same pots 44.25 inches; or as 100 to 127. The self-fertilised plants in Pots 3 and 4 were in every respect very much finer than the crossed plants.

I was so much surprised at this great superiority of the self-fertilised over the crossed plants, that I determined to try how they would behave in one of the pots during a second growth. The two plants, therefore, in Pot 1 were cut down, and repotted without being disturbed in a much larger pot. In the following year the self-fertilised plant showed even a greater superiority than before; for the two tallest flower-stems produced by the one crossed plant were only 29 4/8 and 30 1/8 inches in height, whereas the two tallest stems on the one self-fertilised plant were 49 4/8 and 49 6/8 inches; and this gives a ratio of 100 to 167. Considering all the evidence, there can be no doubt that these self-fertilised plants had a great superiority over the crossed plants.

CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.

TABLE 5/71. Lobelia fulgens (Second Generation).

Heights of flower-stems measured in inches.

Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 27 3/8 : 32 3/8. Pot 1 : 26 : 26 3/8. Pot 1 : 24 3/8 : 25 1/8. Pot 1 : 24 4/8 : 26 2/8.
Pot 2 : 34 : 36 2/8. Pot 2 : 26 6/8 : 28 6/8. Pot 2 : 25 1/8 : 30 1/8. Pot 2 : 26 : 32 2/8.
Pot 3 : 40 4/8 : 30 4/8. Pot 3 : 37 5/8 : 28 2/8. Pot 3 : 32 1/8 : 23.
Pot 4 : 34 5/8 : 29 4/8. Pot 4 : 32 2/8 : 28 3/8. Pot 4 : 29 3/8 : 26. Pot 4 : 27 1/8 : 25 2/8.
Pot 5 : 28 1/8 : 29. Pot 5 : 27 : 24 6/8. Pot 5 : 25 3/8 : 23 2/8. Pot 5 : 24 3/8 : 24.
Pot 6 : 33 5/8 : 44 2/8. Pot 6 : 32 : 37 6/8. Pot 6 : 26 1/8 : 37. Pot 6 : 25 : 35.
Pot 7 : 30 6/8 : 27 2/8. Pot 7 : 30 3/8 : 19 2/8. Pot 7 : 29 2/8 : 21.
Pot 8 : 39 3/8 : 23 1/8. Pot 8 : 37 2/8 : 23 4/8. Pot 8 : 36 : 25 4/8. Pot 8 : 36 : 25 1/8.
Pot 9 : 33 3/8 : 19 3/8. Pot 9 : 25 : 16 3/8. Pot 9 : 25 3/8 : 19. Pot 9 : 21 7/8 : 18 6/8.
Total : 1014.00 : 921.63.

I determined on this occasion to avoid the error of using pollen of not quite equal maturity for crossing and self-fertilisation; so that I squeezed pollen out of the conjoined anthers of young flowers for both operations. Several flowers on the crossed plant in Pot 1 in Table 5/70 were again crossed with pollen from a distinct plant. Several other flowers on the self-fertilised plant in the same pot were again self-fertilised with pollen from the anthers of other flowers on the SAME PLANT. Therefore the degree of self-fertilisation was not quite so close as in the last generation, in which pollen from the SAME FLOWER, kept in paper, was used. These two lots of seeds were thinly sown on opposite sides of nine pots; and the young seedlings were thinned, an equal number of nearly as possible the same age being left on the two sides. In the spring of the following year (1870), when the seedlings had grown to a considerable size, they were measured to the tips of their leaves; and the twenty-three crossed plants averaged 14.04 inches in height, whilst the twenty-three self-fertilised seedlings were 13.54 inches; or as 100 to 96.

In the summer of the same year several of these plants flowered, the crossed and self-fertilised plants flowering almost simultaneously, and all the flower-stems were measured. Those produced by eleven of the crossed plants averaged 30.71 inches, and those by nine of the self-fertilised plants 29.43 inches in height; or as 100 to 96.

The plants in these nine pots, after they had flowered, were repotted without being disturbed in much larger pots; and in the following year, 1871, all flowered freely; but they had grown into such an entangled mass, that the separate plants on each side could no longer be distinguished. Accordingly three or four of the tallest flower-stems on each side of each pot were measured; and the measurements in Table 5/71 are, I think, more trustworthy than the previous ones, from being more numerous, and from the plants being well established and growing vigorously.

The average height of the thirty-four tallest flower-stems on the twenty-three crossed plants is 29.82 inches, and that of the same number of flower-stems on the same number of self-fertilised plants is 27.10 inches, or as 100 to 91. So that the crossed plants now showed a decided advantage over their self-fertilised opponents.

22. POLEMONIACEAE.—Nemophila insignis.

Twelve flowers were crossed with pollen from a distinct plant, but produced only six capsules, containing on an average 18.3 seeds. Eighteen flowers were fertilised with their own pollen and produced ten capsules, containing on an average 12.7 seeds, so that the seeds per capsule were as 100 to 69. (5/25. Several species of Polemoniaceae are known to be proterandrous, but I did not attend to this point in Nemophila. Verlot says ‘Des Variétés’ 1865 page 66, that varieties growing near one another spontaneously intercross.) The crossed seeds weighed a little less than an equal number of self-fertilised seeds, in the proportion of 100 to 105; but this was clearly due to some of the self-fertilised capsules containing very few seeds, and these were much bulkier than the others, from having been better nourished. A subsequent comparison of the number of seeds in a few capsules did not show so great a superiority on the side of the crossed capsules as in the present case.

The seeds were placed on sand, and after germinating were planted in pairs on the opposite sides of five pots, which were kept in the greenhouse. When the seedlings were from 2 to 3 inches in height, most of the crossed had a slight advantage over the self-fertilised. The plants were trained up sticks, and thus grew to a considerable height. In four out of the five pots a crossed plant flowered before any one of the self-fertilised. The plants were first measured to the tips of their leaves, before they had flowered and when the crossed were under a foot in height. The twelve crossed plants averaged 11.1 inches in height, whilst the twelve self-fertilised were less than half of this height, namely, 5.45; or as 100 to 49. Before the plants had grown to their full height, two of the self-fertilised died, and as I feared that this might happen with others, they were again measured to the tops of their stems, as shown in Table 5/72.

TABLE 5/72. Nemophila insignis; 0 means that the plant died.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 32 4/8 : 21 2/8.
Pot 2 : 34 4/8 : 23 5/8.
Pot 3 : 33 1/8 : 19. Pot 3 : 22 2/8 : 7 2/8. Pot 3 : 29 : 17 4/8.
Pot 4 : 35 4/8 : 10 4/8. Pot 4 : 33 4/8 : 27.
Pot 5 : 35 : 0. Pot 5 : 38 : 18 3/8. Pot 5 : 36 : 20 4/8. Pot 5 : 37 4/8 : 34. Pot 5 : 32 4/8 : 0.
Total : 399.38 : 199.00.

The twelve crossed plants now averaged 33.28, and the ten self-fertilised 19.9 inches in height, or as 100 to 60; so that they differed somewhat less than before.

The plants in Pots 3 and 5 were placed under a net in the greenhouse, two of the crossed plants in the latter pot being pulled up on account of the death of two of the self-fertilised; so that altogether six crossed and six self-fertilised plants were left to fertilise themselves spontaneously. The pots were rather small, and the plants did not produce many capsules. The small size of the self-fertilised plants will largely account for the fewness of the capsules which they produced. The six crossed plants bore 105, and the six self-fertilised only 30 capsules; or as 100 to 29.

The self-fertilised seeds thus obtained from the crossed and self-fertilised plants, after germinating on sand, were planted on the opposite sides of four small pots, and treated as before. But many of the plants were unhealthy, and their heights were so unequal—some on both sides being five times as tall as the others—that the averages deduced from the measurements in Table 5/73 are not in the least trustworthy. Nevertheless I have felt bound to give them, as they are opposed to my general conclusions.

The seven self-fertilised plants from the crossed plants here average 15.73, and the seven self-fertilised from the self-fertilised 21 inches in height; or as 100 to 133. Strictly analogous experiments with Viola tricolor and Lathyrus odoratus gave a very different result.

TABLE 5/73. Nemophila insignis.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Self-fertilised Plants from Crossed Plants.
Column 3: Self-fertilised Plants from Self-fertilised Plants.
Pot 1 : 27 : 27 4/8. Pot 1 : 14 : 34 2/8.
Pot 2 : 17 6/8 : 23. Pot 2 : 24 4/8 : 32.
Pot 3 : 16 : 7.
Pot 4 : 5 3/8 : 7 2/8. Pot 4 : 5 4/8 : 16.
Total : 110.13 : 147.00.

23. BORAGINACEAE.—Borago officinalis.

This plant is frequented by a greater number of bees than any other one which I have observed. It is strongly proterandrous (H. Muller ‘Befruchtung’ etc. page 267), and the flowers can hardly fail to be cross-fertilised; but should this not occur, they are capable of self-fertilisation to a limited extent, as some pollen long remains within the anthers, and is apt to fall on the mature stigma. In the year 1863 I covered up a plant, and examined thirty-five flowers, of which only twelve yielded any seeds; whereas of thirty-five flowers on an exposed plant growing close by, all with the exception of two yielded seeds. The covered-up plant, however, produced altogether twenty-five spontaneously self-fertilised seeds; the exposed plant producing fifty-five seeds, the product, no doubt, of cross-fertilisation.

In the year 1868 eighteen flowers on a protected plant were crossed with pollen from a distinct plant, but only seven of these produced fruit; and I suspect that I applied pollen to many of the stigmas before they were mature. These fruits contained on an average 2 seeds, with a maximum in one of three seeds. Twenty-four spontaneously self-fertilised fruits were produced by the same plant, and these contained on an average 1.2 seeds, with a maximum of two in one fruit. So that the fruits from the artificially crossed flowers yielded seeds compared with those from the spontaneously self-fertilised flowers, in the ratio of 100 to 60. But the self-fertilised seeds, as often occurs when few are produced, were heavier than the crossed seeds in the ratio of 100 to 90.

These two lots of seeds were sown on opposite sides of two large pots; but I succeeded in raising only four pairs of equal age. When the seedlings on both sides were about 8 inches in height they were equal. When in full flower they were measured, as follows:—

TABLE 5/74. Borago officinalis.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 19 : 13 4/8. Pot 1 : 21 : 18 6/8. Pot 1 : 16 4/8 : 20 2/8.
Pot 2 : 26 2/8 : 32 2/8.
Total : 82.75 : 84.75.

The average height of the four crossed plants is here 20.68, and that of the four self-fertilised 21.18 inches; or as 100 to 102. The self-fertilised plants thus exceeded the crossed in height by a little; but this was entirely due to the tallness of one of the self-fertilised. The crossed plants in both pots flowered before the self-fertilised. Therefore I believe if more plants had been raised, the result would have been different. I regret that I did not attend to the fertility of the two lots.

24. NOLANACEAE.—Nolana prostrata.

In some of the flowers the stamens are considerably shorter than the pistil, in others equal to it in length. I suspected, therefore, but erroneously as it proved, that this plant was dimorphic, like Primula, Linum, etc., and in the year 1862 twelve plants, covered by a net in the greenhouse, were subjected to trial. The spontaneously self-fertilised flowers yielded 64 grains weight of seeds, but the product of fourteen artificially crossed flowers is here included, which falsely increases the weight of the self-fertilised seeds. Nine uncovered plants, the flowers of which were eagerly visited by bees for their pollen and were no doubt intercrossed by them, produced 79 grains weight of seeds: therefore twelve plants thus treated would have yielded 105 grains. Thus the seeds produced by the flowers on an equal number of plants, when crossed by bees, and spontaneously self-fertilised (the product of fourteen artificially crossed flowers being, however, included in the latter) were in weight as 100 to 61.

In the summer of 1867 the trial was repeated; thirty flowers were crossed with pollen from a distinct plant and produced twenty-seven capsules, each containing five seeds. Thirty-two flowers were fertilised with their own pollen, and produced only six capsules, each with five seeds. So that the crossed and self-fertilised capsules contained the same number of seeds, though many more capsules were produced by the cross-fertilised than by the self-fertilised flowers, in the ratio of 100 to 21.

An equal number of seeds of both lots were weighed, and the crossed seeds were to the self-fertilised in weight as 100 to 82. Therefore a cross increases the number of capsules produced and the weight of the seeds, but not the number of seeds in each capsule.

These two lots of seeds, after germinating on sand, were planted on the opposite sides of three pots. The seedlings when from 6 to 7 inches in height were equal. The plants were measured when fully grown, but their heights were so unequal in the several pots, that the result cannot be fully trusted.

TABLE 5/75. Nolana prostrata.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 8 4/8 : 4 2/8. Pot 1 : 6 4/8 : 7 4/8.
Pot 2 : 10 4/8 : 14 4/8. Pot 2 : 18 : 18.
Pot 3 : 20 2/8 : 22 6/8.
Total : 63.75 : 67.00.

The five crossed plants average 12.75, and the five self-fertilised 13.4 inches in height; or as 100 to 105

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