304 HOW CROPS GROW. 
buckwheat, flax, and tobacco, contain an endosperm. The 
seeds of nearly all other exogenous agricultural plants are 
destitute of an endosperm, and, exclusive of the coats, 
consist entirely of embryo. Such are the seeds of the Le- 
guminosz, viz., the bean, pea, and clover; of the Crucif- 
ere, viz., turnip, radish, and cabbage; of ordinary fruits, 
the apple, pear, cherry, plum, and peach; of the gourd 
family, viz., the pumpkin, melon and cucumber; and finally 
of many hard-wooded trees, viz., the oak, maple, elm, 
birch, and beech. — 
‘We may best observe the structure of the two-cotyle- 
doned embryo in the garden or kidney-bean. After a bean 
has been soaked in warm water for several hours, the coats 
may be easily removed, and the two fleshy cotyledons, c, 
¢, in fig. 64, are found divided from each other save at the 
point where the radicle, a, is seen projecting like a blunt 
spur. On carefully breaking away 
one of the cotyledons, we get a side 
view of the radicle, a, and plumule,d, 
the former of which was partially and 
the latter entirely imbedded between 
the cotyledons. The plumule plainly 
Big: BS exhibits two delicate leaves, on which 
the unaided eye may note the veins. These leaves are 
folded together along their mid-ribs, and may be opened 
and spread out with help of a needle. 
When the kidney-bean (Phaseolus) germinates, the cot- 
yledons are carried up into the air, where they become 
green and constitute the first pair of leaves of the new 
plant. The second pair are the tiny leaves of the plumule 
just described, between which is the bud, whence all the 
subsequent aerial organs develope in succession. 
In the horse-bean, (faba), as in the pea, the cotyledons 
never assume the office of leaves, but remain in the soil and 
gradually yield a large share of their contents to the 
