BEPBODUCTIVE ORGANS OP PLANTS. 333 



pear 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 mag- 

 nifier. 



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 endoge- 

 nous or inside-growing stems (p. 290). 



The seeds of the Exogens (outside-growers p. 296) are 

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

 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 Leguminosae, viz. , the bean, pea, and clover ; of 

 the Cruciferae, viz., turnip, radish, and cabbage ; of ordi- 

 nary fruits, the apple, pear, cherry, plum, and peach ; of 

 the Gourd family, viz., the pumpkin, melon and cucum- 

 ber; 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 ordinary 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 separated 

 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 coty- 

 ledons, we get a side view of the radicle, 

 a, and plumule, J, the former of which 

 /a was partially and the latter entirely im- 

 bedded between the cotyledons. The 

 Fig. 64. plumule plainly exhibits two delicate 



leaves, on which the unaided eye may note the veins. 



