POTATO 



457 



them of reserve foods, the chief of which is starch (Fig, 141). 

 Similar tuber-bearing shoots may also arise from buds in the 

 axils of the foliage leaves above the cotyledons. 



The thin part of the underground rhizomes bear scale-like 

 leaves, and these are also present on the young tubers, but 

 eventually shrivel up before the latter are ripe. Usually only 



Fig. 138. 



Potato seed germinating. 



Section through the same, showing position 



of cotyledons and endosperm (shaded). 

 Seedling nearly free from seed-coat. 

 Seedling quite free (lo days' old) ; a hypo- 



cotyl ; b root ; c cotyledons. . 



Fig. 139. 



Potato seedling (16 

 days old), later stage of 4, 

 in previous Fig., showing 

 plumule e. The coty- 

 ledons c have become 

 broader ; a hypocoty! ; 

 b root. (Natural size.) 



one tuber is developed at the end of a rhizome in seedling 

 plants. Sometimes, however, lateral branches which bear 

 tubers are produced from the axils of the scaly leaves of the 

 rhizomes. 



At the end of the growing season the stems and leaves above 



