PROPAGATION BY SEEDS 



41 



--PLUMULE 

 -CAULICLE 



COTYLEDON 



develop into the root system, and the other end (the plumule) 

 will form the stem and foliage of the plant. 



When the pea is planted, the cotyledons stay in the ground 

 and, in supplying the young growing plant with food, they 

 shrink and become wrinkled. The plumule pushes its way 

 up through the soil to form the stem and leaves of the 

 plant, while the caulicle grows downward, forming the root 

 system. 



51. The bean. All the 

 parts of the seed found in 

 the pea are present in the 

 bean (Fig. 21). The two 

 little leaves in the plumule 

 of the bean can be seen 

 clearly with a small magni- 

 fying glass. The cotyledons, 

 like those of the pea, contain 

 an abundance of stored food 

 material to supply the young 

 plant until it becomes estab- 

 lished. The growth of the 

 bean, however, differs from 

 that of the pea in several 

 respects. The cotyledons of 

 the bean do not stay in the 

 ground but are brought up on the stem into the air, where they 

 turn green and function as leaves for a short time before they 

 finally drop off. Some botanists consider that because the 

 cotyledons function for a time as leaves, they are part of the 

 embryo. Others think that they are not part of the embryo 

 because they are not present on the fully developed plant. 

 In the bean the plumule forms the part of the top above the 

 cotyledons, while the caulicle forms both the root system and 

 the part of the stem extending from the cotyledons to the 

 roots. 



HILUM 

 MICROPYLE 



FIG. 21. The bean seed. A, Exterior view 

 of bean; B, two flat surfaces of bean 

 after testa has been removed. 



