HOW PLANTS OBTAIN THEIR FOOD. 



101 



209. Parts of the pumpkin seedling. During the germination 

 of the seed all parts of the embryo have enlarged. This in- 

 crease in size of a plant is one of the peculiarities of growth. 

 The cotyledons have elongated and expanded somewhat, though 

 not to such a great extent as the root and the stem. The 

 cotyledons also have become green on exposure to the light. 

 Very soon after the main root has emerged from the seed coats, 

 other lateral roots begin to form, so that the 

 root soon becomes very much branched. 

 The main root with its branches makes 

 up the root system of the seedling. Be- 

 tween the expanded cotyledons is seen 

 the plumule. This has enlarged some- 

 what, but not nearly so much as the root, 

 or the part of the stem which extends 

 below the cotyledons. This part of the 

 stem, i.e., that 

 part below the 

 cotyledons and 

 extending to the 

 beginning of the 

 root, is called in 

 all seedlings the 

 hypocotyl, which means " below the cotyledon." 



210. The common garden bean. The common garden bean 

 or the lima bean, may be used for study. The garden bean is 

 not so flattened or broadened as the lima bean. It is rounded- 

 compressed, elongate slightly curved, slightly concave on one 

 side and convex on the other, and the ends are rounded. At 

 the middle of the concave side note the distinct scar (the hilum) 

 formed where the bean seed separates from its attachment to 

 the wall of the pod. Upon one side of this scar is a slight prom- 

 inence which is continued for a short distance toward the end 

 of the bean in the form of a slight ridge. This is the raphe, and 

 represents that part of the stalk of the ovule which is joined to 

 the side of the ovule when the latter is curved around against it 



Fig. 90. 

 Pumpkin seedling rising from the ground. 



