MEMOIRS FROM THE DEPARTMENT OF BOTANY OF COLUMBIA COLLEGE. 167 



cylinder and the xylem make the pleromatic part a strong sheath measuring from 

 100 to 350 II. 



The cuticle is conspicuously ribbed or longitudinally furrowed between the epider- 

 mal elements. The epidermis is composed of one row of oblong-prismatic cells, which in 

 cross section are quite irregular, and the long diameter is often radial, in this, as well as 

 in their irregular prismatic shape, differing from most of the other species examined; 

 their height varies from 50-70 [j.. Trichomes occur as long bristle-like hairs, are unicell- 

 ular and more or less curved upward. 



The periblematic cylinder follows the epidermis, and is easily distinguished from the 

 latter on the one hand and the plerome derivatives on the other. The primary cortex, 

 excepting the starch-ring, is made up of from three to seven layers of cells, which are 

 prismatic, varying from 70-160 [i in height, and in cross section have a diameter varying 

 from 5-40 n, appearing irregular and rather angular or vermiform and near the epidermis 

 are placed with their long axes radial, while further in they lie in the normal position. 

 The starch-ring is conspicuous in both cross and long section. It consists normally of one 

 layer of cells, but between the bundles it often increases to a thickness of three ; the cells 

 are cylindric or prismatic, having a diameter of from 10-60 fi and a height ranging from 

 70-150 ^, and are strikingly larger than the neighboring elements of the primary cortex. 



The pleromatic cylinder has all its parts well developed. The stereome is composed 

 of prismatic stereids, with rounded angles in cross section, forming a sheath one to four 

 cells deep. The cells are from 10-40 [i in diameter and 200-300 fj. high. The cylinder 

 is continuous and most compact at the outside of the bundles, while between the latter 

 the cells are larger and not as closely packed, and as is the case in section Bistorta, the 

 septa are almost invariably transverse. The phloem is conspicuous as narrow fascicles 

 toward the outer sides of the bundles. Between the latter it is interrupted for short 

 distances by the intrusion of the stereome cylinder. The sieve-tubes and cells of the 

 phloem are prismatic and in cross section appear quite angular, measuring from 5-10 fi 

 in diameter; in favorable sections they are distinct and vary in length from 100-160 fi. 

 The woody fibres in cross section are either square or oblong, and lie with their short axes 

 radial. They are smallest and most compactly arranged at the centers of the bundles, 

 and range from 5-10 (i in diameter. The ends are either oblique or tapering. As in 

 the preceding subgenus, the tracheides and vessels occur normally along a line on either 

 side of which the woody fibres and protoxylem are respectively situated. These large 

 elements of the tracheae measure from 30-70 (j. in di£|,meter and are either nearly circular 

 in cross section or somewhat prismatic. In long section various combinations of the 

 tracheides and vessels are found. Four different kinds are sometimes met with as repre- 



