﻿I9i6] MCCORMICK— IPOMOEA BATATAS 393 



exception, the material was killed in chromo-acetic and imbedded 

 in paraffin. Young tubers were cut in serial sections, beginning 

 at the stem and extending beyond the region of greatest thick- 

 ening of the root. With the exception of fig. 1, all figures are 



Fig. 4. — Transverse section of stele of root showing separation of xylem by 

 parenchyma: px, protoxylem; st, sieve tube; sx, secondary xylem; Xi55- 



intentionally from the same tuber, but sections from many other 

 tubers verify the essential features of the results here given. Some 

 distortion must necessarily accompany such localized and greatly 

 increased amount of thickening, but in that respect only does the 

 structure of the fully matured tuber differ from that shown in 



