“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. “The coöperation of air is not less necessary. Seeds might have the proper temperature and sufficient moisture, but if air were lacking germination would not follow. This capital condition explains to us why seeds planted too deep fail to come up; why germination is much easier in soil that is mellow and can be permeated by the air than in soil that is compact; why delicate seeds should be covered with very little earth or even simply sown on the surface of the moist ground; and, finally, why ground on being broken often becomes covered with fresh vegetation from the sprouting of seeds that have for years lain dormant in the soil, needing only to be stirred up and brought into contact with the air in order to germinate. “Under like conditions of temperature, moisture, and air, by no means all seeds require the same length of time for germinating. Common garden cress germinates in about two days. Spinach, turnips, and beans take three days to come up; lettuce, four; melons and pumpkins, five; cereals, about a week. Two years and sometimes more are needed by the rose-bush, the hawthorn, and various stone-fruit trees. Generally seeds with thick and hard shells are slow in germinating on account of the obstacle they oppose to the penetration of moisture. Finally, when sown fresh, immediately after coming to maturity, seeds germinate quicker than when old, because old seeds have to recover by a prolonged sojourn in the ground the moisture lost through prolonged drying.