﻿MCCORMICK— IPOMOEA BATATAS 



397 



a mature tuber strands of phloem unaccompanied by xylem are 

 common. 



In the young roots of /. Batatas the laticiferous cells are sharply 

 delimited; but in the older tubers, in which the parenchyma cells 

 are larger, they are not readily distinguished. The cross-walls 

 are numerous and are not resorbed. 



Summary 



1. The larger roots of Ipomoea Batatas Lam. are polyarch, 

 chiefly pentarch and hexarch. 



2. Secondary thickenings occur in the usual way and there is 

 formed a massive structure of secondary xylem. 



3. Secondary cambiums are organized around strands of xylem 

 and phloem which are separated by thin-walled parenchymatous 

 cells. The primary and secondary cambiums are capable of forming 

 xylem and phloem in isolated strands. One may reasonably 

 expect that, if the conditions for growth are especially favorable, 

 the secondary cambiums may be organized earlier. 



4. A section of a mature tuber shows a structure consisting 

 chiefly of parenchyma, and mingled with the parenchyma are 

 strands of xylem, which consist of one to several vessels, and may 

 or may not be accompanied by phloem. Each strand is sur- 

 rounded by a cambium. There may also be seen strands of phloem 

 unaccompanied by xylem. This structure may be definitely traced 

 back to the radial protostele. 



The writer wishes to express acknowledgments to Dr. W. J. G. 

 Land for some valuable help given at the beginning of the investi- 

 gation. 



Agricultural Experiment Station 

 Lincoln, Neb. 



LITERATURE CITED 



1. Choisy, J. D., DeCandolle's Prodr. 9:338- 1845- 



2. Czapek, F., Zur Kenntniss des Milchsaftsystems der Convolvulaceae. 

 Sitzungsb. K. Akad. Wiss. Wein 103:87-121. 1894. 



3- DeBary, A., Comparative anatomy of phanerogams and ferns. 1884. 

 4. DeCandolle, Alph., Origin of cultivated plants. 1885 (p. 54). 



