With an ordinary magnifyirig-glass the tiny plantlet is not difficult to discover compactly folded up within the seed. If we place seeds of pumpkin, bean, corn, or pea in boiling water until fully swelled, and then carefully dissect them, we will soon find the embryo plantlet which exists in all seeds grown by the horticulturist. What is known as sprouting or germination is merely the unfolding and growth of the embryotic plant. Some of the soil requisites and other favoring conditions for germination have been given in the preceding chapter. The mature seed contains starch or protoplasm in dormant condition. When placed in moist soil, with temperature suited to the variety or species, the protoplasm becomes active, as when the spring awakens activity of circulation and growth of dormant trees in spring.
The cells of the embryo begin to increase in number by division, and soon the tiny shoot, known popularly as the sprout and by botanists as the hypocotyl, starts downward. If the seed is not properly placed, this first growth will make a curve before the rounded point extends downward. In the forest we often see the acorn, lying on moist leaves, project the hypocotyl through the leaves to the moist earth, and later, when fastened to the soil, the up-growing shoot, known as the plumule, starts. All seeds start the root or hypocotyl downward prior to the starting of the plumule upward to be exposed to the air and sun.
Germination is said to be completed when the young plantlet forms perfect leaves and is capable of living without additional support from the stored nutriment in the seed.