REPRODUCTIVE ORGANS OF PLANTS. 303 



the other grains is the embryo. Its form is with difficulty 

 distinguishable in the dry seeds, but when they have been 

 soaked for several days in water, it is readily removed 

 from the accompanying endosperm, and plainly exhibits 

 its three parts, viz., the radicle, the plumule, and the 

 cotyledon. 



In fig. 63 is represented the embryo of maize. In A 

 and B it is seen in section imbedded in the endosperm. 

 C exhibits the detached embryo. The Radicle, r, is the 

 rootlet of the seed-plant, or rather the point from which 

 downward growth proceeds, from which the first true roots 

 are produced. The Plumule, c, is the ascending axis of 

 the plant, the central bud, out of which the stem with new 

 leaves, flowers, etc., is developed. The Cotyledon, b, is 

 in structure a ready-formed leaf, wliich clasps the plumule 

 in the embryo, as the 

 proper leaves clasp the 

 stem in the mature 

 maize-plant. The coty- 

 ledon of maize does not, 

 however, perform the 

 functions of a leaf; on 



the contrary, it remains in the soil during the act of sprout- 

 ing, and its contents, like those of the endosperm, are 

 absorbed by the plumule and radicle. The leaves which 

 appear above-ground, in the case of maize and the other 

 grains (buckwheat excepted,) are those which in the 

 embryo were wrapped together in the plumule, where they 

 can be plainly distinguished by the aid of a magnifier. 



It will be noticed that the true grains (which have 

 sheathing leaves and hollow jointed stems) are monocot- 

 yledonous (one-cotyledoned) in the seed. As has been 

 mentioned, this is characteristic of plants with Endogenous 

 or inside-growing stems, (p. 268.) 



The seeds of the Exogens (outside-growers) (p. 273) are 

 dicotyledonous, i. c., have two cotyledons. Those of 



