4^0 



SOLANACE^ 



are arranged spirally. At the ' rose ' end, or the morphological 

 apex of the tuber, the ' eyes ' are more crowded together than at 



its ' heel ' or base, the older 

 internodes being longer than 

 the younger ones. Each 'eye ' 

 appears as a collection of buds 

 lying more or less in a de- 

 pression; the latter is the 

 axil of a scaly leaf which was 

 visible when the tuber was 

 young, but now withered up 

 and lost. The number of 

 buds in each 'eye' may be as 

 many as twenty, but three is 

 the usual number. 



In reality the ' eye ' is a 

 lateral branch with unde- 



FlG. 142. — Leafy stem of potato, showing tuber . , . , , , . 



growing in the axils of an ordinary leaf, a Tuber VelOpeQ mtemOdeS, the WhOle 



in axil of leaf £^; b two more branches in same . -. 1 • «„.„n„„ ^:„l,l„ 



leaf-axil ; c branch beginning to develop into a tubei bcmg generally a riChly 



tuber in axil of leaf.. branched shoot-system and 



not a simple shoot. 



Tubers are not always of the same form ; three moderately 

 distinct and fairly constant types are prevalent, namely, (i) 

 'round,' (2) 'oval,' and (3) 'kidney' shapes. The round 

 type is somewhat spherical, and has fewer internodes and ' eyes' 

 than (2) and (3), both of which are elongated. The kidney 

 potatoes are thickest at the ' rose ' end and taper towards the 

 ' heel,' while the oval varieties are thickest in the middle and 

 taper towards both ends. Those differences are sufficiently 

 marked and constant to form a basis of classification of the 

 varieties in cultivation. 



In some instances the tubers are of very irregular shape. 

 When long-continued dry weather checks vegetation, and is 

 followed by rains, the partially-ripened tubers, instead of 



