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- 

 guminosae, viz., the bean, pea, and clover; of the Crucif- 

 erse, 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, 

 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,^, 

 the former of which was partially and 

 the latter entirely imbedded between 

 the cotyledons. The plumule plainly 

 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 



