“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.” [[138]]
CHAPTER XXIX
GERMINATION
“The germ in the heart of the seed is in a state that may be likened to deep sleep: its life is, as it were, arrested, suspended. But under the stimulus of certain conditions it awakens, throws off its coverings, gathers strength from its stored-up food, unfolds its first leaves, and appears above ground. This opening of the seed is called germination. Moisture, warmth, and air are the determining causes; without their coöperation the seed would remain a certain length of time in good condition for sowing, after which it would wither and lose its germinating power.
“No seed germinates without the help of moisture. Water plays a multiple part. First it soaks into the germ and the parts surrounding it, causing these to swell more than the envelope, so that the latter, however hard a shell it may be, is burst open. Through the cracks of this broken envelope the gemmule pushes out on one side and the radicle on the other, and henceforth the little plant enjoys the benefit of sun and air. Germination is more or less slow according to the degree of resistance offered by the walls of the seed. If these are hard and stony it is only with extreme slowness that the germ absorbs [[139]]moisture and manages to burst its cell. Therefore, to shorten the period of germination care is taken to thin the shells of excessively hard seeds by rubbing them with a stone.
“Besides the mechanical part played by water in opening the seed, it has still another relating to nutrition. The various changes undergone by the alimentary contents of the perisperm and the cotyledons in becoming liquefied and capable of absorption cannot take place without the aid of water. Furthermore, this liquid is indispensable for dissolving the nutritive ingredients, introducing them into the young plant, and distributing them evenly throughout. It is plain, then, that if the seed remains dry it is absolutely impossible for it to germinate, and that in order to preserve seeds the first condition is to protect them from moisture.
“With moisture there must also be warmth. As a general rule, germination proceeds most satisfactorily when the thermometer registers between ten and twenty degrees centigrade, our spring and autumn temperature. Outside these limits, be it above or below, germination is retarded, ceasing altogether in extreme temperatures.