REPRODUCTIVE ORGANS OF PLANTS. 303 
the other grains is theembryo. 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 Plumade, 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, }, is 
in structure a ready-formed leaf, which 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 Hxogens (outside-growers) (p. 273) are 
dicotyledonous, i. e., have two cotyledons. Those of 
Fig. 63. 
