THE STALK OF THE PLANT

Field, Forest and Farm by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. THE STALK OF THE PLANT

CHAPTER XIV. THE STALK OF THE PLANT

“The stalk is the common support of the plant’s various parts. It is called annual or herbaceous when it lives only one year, as in the potato, spinach, parsley, and all forms of vegetation that from their soft structure belong to the class of herbs. Ligneous is the name given to the stalk when, designed to live for a greater or less number of years, it is made of strong woody fibers, such as we find in the trunks of trees.

“Let us make a clean cut through any tree-trunk, that of an oak for example. We shall find it divided into three parts: in the center the pith or marrow, very slightly developed; around the marrow the wood proper; and, finally, on the outside, the bark. A closer examination shows that the wood is formed of concentric layers which are indicated in the cross-section by a series of circles having the marrow for a common center. These layers are called ligneous zones or, since one is formed every year, annual layers. During the summer there is a downward flow, throughout the tree, of a peculiar liquid, the descending sap, which constitutes the fluid nourishment of the tree. This liquid runs between the wood and the bark and becomes, little by little in its course, [71]on one side a layer of wood which attaches itself to the outer surface of the preceding year’s layer, and on the other side a thin sheet of bark which is added to the inner surface of the bark already formed.

“Thus each year both bark and wood form a new layer; but this added layer is applied in opposite ways in the two instances,—outside on the wood, inside on the bark. The wood thus encircled from year to year by new layers increases in age toward the center and becomes younger and younger toward the circumference, whereas the bark, lined every year with a fresh sheet, shows its youth on the inside and its age on the outside. The first buries inside the trunk its decrepit and dead layers; the second thrusts its old layers outside, where they crack and fall off in large scales. This aging process is simultaneous on the outside and in the center of the tree-trunk; but between the wood and the bark life is always at work, creating fresh accretions.

Cross Section of Tree Trunk

“Here are some experimental proofs of this annual formation of a ligneous layer. A strip of bark is removed from the trunk of a tree, and on the wood thus laid bare is fastened a thin sheet of metal. The bark is then replaced and bound with ligatures so that the wound may heal. We will suppose ten years have passed. The bark is raised again at the same place. The metal sheet is no longer visible; to find it you must bore deep into the wood. Now, [72]if you count the ligneous layers removed before reaching the metal sheet, you will find precisely ten, just the number of years that have passed.

“A number of observations like the following are familiar: Some foresters cut down a beech bearing on its trunk the date 1750. The same inscription was found again in the inner substance of the wood, but to reach it they had to cut through fifty-five layers on which no mark whatever appeared. If now, we add 55 to 1750 we obtain precisely the year when the tree was felled, or 1805. The inscription carved on the trunk in the year 1750 had passed through the bark and reached the layer of wood that was then outermost. Since that event fifty-five years had passed and new layers, exactly the same in number, had grown over the first.

“Thus a tree is composed of a succession of woody sheaths, the outer ones enveloping the inner. The stem or trunk contains them all; the branches, according to their age, contain more or fewer. Each one represents a single year’s growth. The woody sheath of the present year occupies the exterior of the trunk, immediately under the bark; those of former years occupy the interior, and the nearer they are to the center the older they are. The layers of future years will come one at a time and take their places over preceding layers, so that what is now the outermost layer will in its turn be found embedded in the body of the trunk.

“Of all these ligneous zones of unequal age the most important to-day is the outside one; its destruction [73]would cause the death of the tree, since through it the nutritive juices of the earth reach the buds, leaves, and young branches. In their time the interior layers, one by one, when they formed the surface, rendered the same service to the buds of their day; but now that these buds have become branches the inner layers have only a secondary office, or even none at all. Those nearest the outside still have some aptness for work and help the layer of the year to carry the juices from the earth to the branches. As to the innermost ones, they have lost all activity; their wood is hard, dried up, encrusted with inert matter. In their decrepitude these interior layers are incapable of service in the work of vegetation; the most they can do is by the support of their firm woody structure to give solidity to the whole. Thus the tree’s activity decreases from the outside toward the center. On the surface are youth, vigor, labor; in the center old age, ruin, repose.”

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