TUBERS—STARCH

“There are buds that, though called to an independent existence, do not, before separating from the mother plant, store up provisions nor thicken their scales; but the plant itself is charged with feeding them. When it is intended that the stem or branch shall itself maintain the buds it bears, then, instead of coming out into the open air where it would speedily cover itself with foliage and flowers, it remains underground and has for leaves only rudimentary scales. It grows so corpulent and deformed as to cease to bear the name of branch and to take instead that of tuber. As soon as necessary supplies have been stored up, the tuber detaches itself from the mother plant, and thenceforth the buds it bears find in it abundant nourishment for their separate existence. A tuber, then, is an underground branch swollen with nutritive material and having undeveloped scales in place of leaves, and it is also dotted here and there with buds which it must feed.

“Let us now look at a potato. What do we see on the surface? Certain small cavities or eyes; that is to say, so many buds, for these eyes develop into [94]branches if the potato is placed in favorable conditions. On old potatoes, late in the season, the buds are seen to send forth sprouts which need only a little sunshine to turn green and become stalks. Agriculture makes good use of this peculiarity: to propagate the plant it is customary to put into the ground, not the seeds, which would yield no harvest before the lapse of several years, but the tubers, which produce abundantly the same year. Or else the potato is cut into pieces and each piece, planted in the ground, sends up a new plant on condition that it has at least one eye; if it has none it rots without producing anything.

“Furthermore, you can see on the eyes tiny little scales, which are leaves modified to adapt them to an underground life, leaves with the same right to the name as the tough scales of an ordinary bud. Since it has leaves and buds the potato is therefore a branch. Should there remain any lingering doubts on this subject, it might be added that by earthing up the plant, that is to say by heaping soil around the stalk, the young branches thus buried can be converted into potato-bearers; and it might also be added that in rainy and cloudy seasons it is not rare to see some of the ordinary branches thicken and swell up in the open air, and thus produce potatoes more or less perfect. Accordingly the potato is to be regarded as an underground branch swollen with nourishment—in short, a tuber.

“Many other plants produce similar branches that grow under ground. In this number is the Jerusalem artichoke, the tubers of which have buds arranged two by two on opposite swellings, from front to back and from right to left in turn, exactly as are leaves and buds on the stem.

“The potato feeds it buds on a farinaceous substance called fecula or, in less learned language, starch. It is the very material that makes the vegetable so rich in nutriment for us. We turn to our own account what the plant has stored up for its young shoots. Starch is contained in the extremely small cavities with which the flesh of the tuber is all riddled. These cavities are called cells. They are microscopic sacs made of a fine membrane and having no opening. Crammed full of starch grains and crowded one against another, they compose the fleshy substance of the potato. But these cavities are so small that a person would strain his eyes in vain in any attempt to see them in the cross-section of a potato. A magnifying glass is necessary. So minute are the cells that in a piece of potato no larger than a pin’s head there is room for dozens and dozens of them. This picture shows you, but much larger than in nature, a potato cell with the grains of starch it encloses.”

Starch Grains of Potato

“How beautifully,” exclaimed Emile, “those grains of starch are arranged in their little cubby-hole! They might be taken for a nest of eggs. And you say there are heaps and heaps of these little starch cells?”[96]

“Yes, my boy; in a medium-sized potato they could be counted by millions and millions.”

“It must be rather a curious sight to look at a little piece of potato through a powerful magnifying-glass.”

“It is indeed one of the most curious sights, this countless multitude of starch grains, all the same shape, all white as snow, gathered together by tens, dozens, scores, and even more, in their delicate little box-like cells.

“Let us perform an experiment not beyond our means; let us remove the starch from a potato. All we need to do is to tear open the cells in order to liberate the starch grains, and then filter them out. Watch me do it. With a kitchen grater I reduce the potato to pulp and thus tear the cells open. Now I put the pulp on a piece of linen over a large glass and pour a little water through it with one hand while with the other I keep stirring the pulp. The grains of starch from the ruptured cells are washed away by the water and carried through the meshes of the fabric, while the remnants of the cell-walls, being too large to pass through, stay behind in the filter.

“Thus I obtain a glassful of turbid water. Look at it under a bright sun. In the water a multitude of white satiny specks are falling like so much snow and piling up on the bottom. In a few moments the deposit has settled. I then throw away the clear water above it and have left a powdery substance, magnificently white, which if pressed between the [97]fingers creaks like fine sand. It is the starch of the potato, and is made up of such fine grains that it would take from one hundred and fifty to two hundred to equal the head of a pin in size. Nevertheless these grains, minute though they are, have a very complicated structure, each one of them being composed of a large number of tiny leaflets folded one over another. The picture I showed you just now will serve to give you an idea of these superposed leaflets that go to make, all together, a single grain. Now if some of this starch is boiled in a little water, the successive leaflets of the grain open and separate, and the whole becomes an unctuous jelly far exceeding in volume that of the starch used.”

To prove this assertion, Uncle Paul proceeded to heat in a little water the starch taken from the potato, and soon the powdery matter was reduced to a beautiful pellucid jelly.