142 REPRODUCTION IN PLANTS AND ANIMALS. 



movements of life again commence those impulses which it 

 received from the parent plant. Th& chick bursts through 

 the egg, impatient of confinement, and the embryo plantule 

 ruptures the integuments of the seed, running through the 

 same phases of development as the plant on which it origi- 

 nated. 



As soon as the seed begins to germinate, the first thing 

 that we notice is the softening and swelling of its envelopes ; 

 its testa or outer covering is ruptured, and the embryo elon- 

 gates downwards by its radicle or young root, and upwards 

 by its plumule or young stem, lifting the cotyledons or seed 

 leaves above the earth's surface. These seed leaves, when 

 exposed to the light, speedily acquire a green hue, and in 

 dicotyledonous embryos ultimately assume the form of two 

 opposite leaves. These leaves are somewhat thick and 

 fleshy, their margin is invariably entire, and they ulti- 

 mately become so altered in appearance, as to be altoge- 

 ther different from what they were when wrapped up 

 within the folds of the testa. If the plant has but one of 

 these leaves, it is called a Monocotyledon, if it has two, a 

 Dicotyledon. Plants that spring up without these appen- 

 dages are called Acotyledons. These last develop, not from 

 seeds, but spores. 



The cotyledonary leaves attached to the embryo contain 

 a store of starch, which contributes to the development of 

 the first pair of atmospheric leaves and also to the extension 

 of the root in the soil ; hence, at the end of a certain time 

 they fade and fall, having discharged their allotted func- 

 tions. The second pair of leaves take the form peculiar to 

 the plant and remain permanently attached to its stem ; as 

 they aerate the fluid absorbed into the interior of the plant 

 by the radicles, much more perfectly than the cotyledon- 



