SOLANUM TUBEROSUM 



511 



Development of the Seedling. — The mature U-shaped embryo 

 lies embedded in the endosperm so that both the tip of the radicle 

 and those of the two cotyledons are directed toward the micro- 

 pyle. (Fig. 175, A.') Upon germination, the radicle emerges 

 from the micropylar end of the seed and grows rapidly to form a 

 tap root which soon produces numerous secondary roots. The 

 hypocotyl elongates, lifting the oval cotyledons above the ground; 



B 



Fig. 2.76. A, habit of young seedling showing development of rhizomes and young tubers 

 at cotyledonary node ; B, enlarged detail of base showing rhizomes and adventitious roots 

 at node. 



and this is followed by the development of the epicotyl from which 

 the first simple, ovate, foliage leaves are differentiated. (Fig. 

 2.71..') 



At this time, the first rhizomes arise in the axils of the cotyle- 

 donary leaves above the ground level. They are slender and 

 cylindrical, possessing small rudimentary leaves; and, after 

 elongating until their tips strike the ground, they penetrate the 

 soil and begin to swell and form tubers. (Fig. X76, A, 5.) Adven- 

 titious roots arise from the rhizomes and the cotyledonary node, 

 and additional rhizomes may develop in the axils of the first 

 foliage leaves. In general, the tubers which are produced the first 



