“I have just told you that many plants have only one cotyledon. I will add that this cotyledon is usually very small. It is especially in these plants that the perisperm is present. The grain of wheat offers a notable illustration of this truth. Cut lengthwise and looked at through a magnifying-glass, this seed would reveal to us what is represented in the picture I now show you. At the bottom and toward one side is the germ, forming but a very small part of the seed. At c is the single cotyledon, whence will come the first leaf, the seminal leaf. At e is the gemmule, which will furnish the next leaves. At the opposite end is a short nipple, the radicle, whence the root will spring. Now compare the tiny cotyledon of the wheat with the two voluminous ones of the almond. The latter, with their rich store of nourishment, will easily be able to feed the young plant until it has vigorous roots; but the cotyledon of the wheat, so poor and slender—can it nourish the young plant? Certainly not. Then the wheat germ must without fail have a storehouse of provisions. This storehouse is the perisperm (pr), a farinaceous mass constituting nearly the whole of the seed. This same perisperm, the first food of the wheat’s first shoot, is also the chief food of man; it is what, under the millstone, becomes flour, of which bread is made. But how can the farinaceous substance of the perisperm nourish the plant? A very simple experiment will show us. Put some wheat in a saucer and keep it slightly moist. In a short time the seed will germinate. As soon as the young sprouts show their green points take one of the grains: you will find it softened all through. You can crush it between your fingers and squeeze out a white fluid, very sweet to the taste and much resembling some sort of milk. What has taken place ought not to be beyond your power to surmise from the account I gave you of the wonderful change starch may undergo. The perisperm of the wheat-grain consists chiefly of starch. During germination this accumulation of starch is converted into a sugary substance, into glucose in fact. Thence comes the sort of plant-milk with which the seed is now swollen. The germ is immersed in this sweet liquid; it imbibes it, soaks it up almost as a fine sponge would; and with the matter thus absorbed it augments its own substance, which lengthens into root, stem, and leaves. With what furnishes us bread the grain of wheat suckles the starting wheat-stalk.” CHAPTER XXXIII CULTIVATED PLANTS “Three modes of plant-propagation are in use among horticulturists, namely: layering, slipping, and grafting. To get an adequate notion of the great usefulness of these operations let us dwell for a moment on the origin of our cultivated plants.