﻿1916] MCCORMICK— 1 POMOEA BATATAS 389 



This is the extent of the literature bearing directly on the 

 anatomy of the tuber of /. Batatas, but other species of the Con- 

 volvulaceae have been studied, and in addition fleshy roots in other 

 families, some of which to a certain degree resemble structurally 

 the fleshy root of I. Batatas. 



In 1870, Van Tieghem (22) studied the roots of Convolvulus 

 tricolor. He states that there are 4 rays of xylem, and that the 

 lateral roots are formed in 4 rows corresponding to these rays. 

 He describes and figures a tetrarch root and also the secondary 

 tissues which are formed later. Here, also, there is a separation 

 of the vessels by thin-walled parenchyma cells, such as may be 

 seen in the early stages of thickening of the root of /. Batatas. 



Schmitz (15), in his extensive study of the roots of the Con- 

 volvulaceae, omitted /. Batatas. Of those which he investigated. 

 Radix Scammonia, the fleshy root of Convolvulus Scammonia, and 

 /. Turpethum most closely resemble /. Batatas. He discusses the 

 laticiferous vessels and states that they develop directly from the 

 cambium and not from sieve tubes, as stated by A. Vogl. 



Weiss (23) did not consider the Convolvulaceae in his studies 

 of fleshy roots, but his descriptions and figures of Bryonia dioica 

 show a concentric arrangement of cambium around strands of 

 xylem, similar to that found in the thickened root of /. Batatas. 



Peterson (13) investigated /. Batatas as to the bicollateral 

 structure of the stem; but he did not discuss the root. He 

 mentions the internal phloem of the stem as being strongly 

 developed, and this feature is also characteristic of the older roots. 



DeBary (3) reviews Schmitz's work, but adds nothing of 

 importance concerning the anatomy. He makes a distinction 

 between the laticiferous tubes, such as are found in the Euphor- 

 biaceae, and the resin sacs of the Convolvulaceae. 



Scott (16), in his paper on the anatomy of Ipomoea versicolor, 

 considers chiefly the anomalous structure found in the transition 

 region between the bicollateral stem and the root. 



Czapek (2) reviews the literature on the laticiferous system in 

 the Convolvulaceae. He studied the development of the system 

 in many species, and, with the exception of Dichondra. he found 

 cross- walls always present. 



