THE SEED’S FOOD-SUPPLY

“When it has leaves and roots that are sufficiently developed, the little almond-tree will nourish itself by drawing what it needs from the earth and air. But until then it must live, it must grow stronger, and it must increase a little in size. As nothing can come from nothing, the germinating seed must find somewhere the material for its first growth. This cannot be in the soil so long as the radicle is nothing but a point, incapable of any work; neither can it be in the air so long as the little leaf-bud has not unfolded and developed into foliage. The seed, then, must have a certain supply of nutriment stored up within itself. Let us turn our attention to this prepared stock of food.

“In the almond we have studied the gemmule or leaf-bud, the radicle, and the tigella; but there still remain two large pieces, easily separable from each other, and constituting by themselves alone almost the entire bulk of the seed. These two pieces are the plant’s first pair of leaves, but leaves of a peculiar structure, being very thick, fleshy, and relatively enormous in size. They are the alimentary reservoirs, the storehouses of food from which in its beginning the young plant must draw its sustenance. [135]When germination begins, these two large leaves, swollen with nutritive matter, yield little by little a part of their substance to the tiny plant and suckle it, as it were. They might therefore be called vegetable udders, nursing-leaves, but science calls them cotyledons. The unhatched chick in its shell has the yolk of the egg to furnish substance for its growth, the young lamb has its mother’s milk, the germ of the plant has the juice of the cotyledons.

“The same structure, with two cotyledons of great size and easy to observe, may be found in the broad bean, pea, kidney bean, and acorn, and in the stones of the peach, apricot, and plum. It would also be found in the pips of pears and apples as well as in the seeds of most of our cultivated plants, but more difficult to distinguish in proportion to the smallness of the seed. In every instance the seed would be found to have two cotyledons as food-storehouses, and also a gemmule and a radicle united by the tigella. Other plants, on the contrary, like maize, wheat, and the other cereals, as also the lily, tulip, and iris, have but one cotyledon, one nursing-leaf for the new vegetable organism.

“It is not always easy, especially when the seed is very small, to ascertain whether it has two cotyledons or only one; but as soon as germination has begun, this difficulty disappears. Then the seed with two cotyledons is seen to push up two leaves, the very first to appear, situated opposite each other, and very often differing in shape from those that come later. In the radish, for example, they are [136]heart-shaped; in the carrot, long and narrow like little tongues. These two leaves that precede the others are known as seminal leaves. They come from the two cotyledons, which generally open in the air and grow green while nourishing the young plant with a part of their substance; but sometimes, as in the acorn, they remain hidden underground. On the other hand, seeds having but one cotyledon come up with only one seminal leaf, generally narrow and long. This is what we observe if we watch the germination of a grain of wheat.

“A simpler and quicker method may be used for ascertaining how many cotyledons a seed has. Hold a leaf up to the light and you will see its texture traversed by a multitude of little cords which serve it as a kind of framework. These cords are called veins or nerves. Now then, if you compare the leaf of a pear-tree with a blade of wheat, or reed, you will see that in the former the veins are more and more subdivided and ramified, joining one another and thus forming a network with irregular meshes, while in the latter the veins do not branch, but run in parallel lines without forming meshes. We should find the same difference of framework between the leaves of the elm, poplar, and plane-tree, on the one hand, and those of the iris, narcissus, and tulip, on the other. This difference being established, I will add that with few exceptions, of no interest to us here, every plant with netted-veined leaves has two cotyledons in its seed, and that every plant with parallel-veined leaves has but one. Consequently [137]it is only necessary to glance at the foliage in order to know whether the seed has two cotyledons or only one. I will say further that pines, firs, and the other resinous trees have as many as ten cotyledons, which show themselves as a delicate tuft of leaves when the little plant comes out of the ground.”

Uncle Paul then led the children into the garden to fix in their minds by observation the lesson they had just learned. “Gather haphazard,” said he, “the first leaves you come to; then examine them and tell me how many cotyledons the seed must contain. First, here is the iris, with large blue flowers and sword-shaped leaves.”

“I see,” said Jules, “veins running in regular lines side by side, without ever joining one another. Since these veins are parallel the iris seed has only one cotyledon.”

“And this blade of grass, this also that I pick from a corn-stalk?” asked his uncle.

“They, too, have parallel veins, both of them; and so their seeds must have only one cotyledon.”

“And this grape-leaf, this leaf of the cherry tree?”

“It’s my turn now,” Emile hastened to interpose. “The veins form a sort of lace with very fine meshes. The grape and the cherry have two cotyledons.”

“It is as easy as that, my friends. The leaf with its arrangement of veins shows us the fundamental characteristics of the plant. It tells us whether the germ is fed by one nursing-leaf or two, whether the young plant comes up with one seminal leaf or two.”