PLATE 4 
Stages in the development of the tuber. 
A. -—Section through periderm, cortex, pericyclic region and vascular ring of mature 
tuber. X4S- 
B. —The same as in A, except that tuber is only io mm. in diameter. X 45 - 
C. —The same as A and B, but tuber is only 2.5 mm. in diameter. 
