108 



GERMINATION OF SEEDS: SEEDLINGS 



cotyledons. Thus most of the stem and all of the leaves, flowers, 

 and fruit of the adult stage are produced by the plumule. 



The cotyledons, which are commonly fleshy in these seedlings, 

 enlarge after reaching the light and their color changes to 

 green, which with the presence of stomata indicates that they 

 function to some extent like ordinary leaves in the manufacture 



of foods. However, it 

 is only a short time till 

 most of them, espe- 

 cially the fleshy ones, 

 begin to show shrink- 

 age which continues as 

 the food is used for 

 growth, until much 

 shriveled and dried 

 they fall from .the 

 plant. In some cases, 

 as in the Buckwheat 

 and Castor Bean where 

 the seeds are albumin- 

 ous, the thin cotyledons 

 are more leaf-like and 

 function like ordina^ 

 leaves for a consider- 

 able time, although in 

 arrangement, shape, or 

 size they are never just 

 like ordinary leaves and 

 never so long-lived. 

 (Fig. 102.} Where the 

 cotyledons are large, 

 much force is required 

 to pull them through 



the soil, and, consequently, when the ground is hard or covered 

 with a crust, seedlings of this type often fail to develop. 



As to how the development of both radicle and plumule pro- 

 ceeds until the adult stage is reached, that depends much upon 

 the kind of plant. In most cases the radicle forms a central root 

 which, although prominent at first, may be much obscured in the 

 adult stage by large secondary roots developing from the base of 



FIG. 102. Seedling of Castor Bean, in which 

 the cotyledons persist and function like leaves 

 for some time. 



