﻿74 



VEGETATIVE FEATURES. 



built by Professor Benjamin Silliman, the first used in America. This mounts 

 a 6-inch saw, and is run by foot power, so that the sections that could be made upon 

 it were far more limited in area than those cut on the Dwight petrotome, which 

 was later most generously given for the work on the fossil cycads by Professors 

 E. S. Dana and G. J. Brush. Nor was the writer at the time of this earlier work 

 acquainted with the stone cements later used. It accordingly did not occur to him 

 to employ the method of double sectioning, later so satisfactorily introduced in the 

 study of fructification. The results described would, in short, be far more com- 

 plete had the sections been large and had the parts resulting from the making of 

 longitudinal sections, with as little loss of material as possible, been then cemented 

 together again in their true position before making the complementary transverse 



Fig. 40.— Cycadeoidea Wielandi Ward. Structure of the xylera zone or woody cylinder of trunk 

 Transverse section through middle of xylem (a) and phloem (b) of S. 260. ■ about I 50. 



393. 



series complete less the saw cuts. The resumption of the study of the cortex after 



the working out of better laboratory methods was, however, on the score of relative 



urgency, deferred. 



XYLEM ZONE. 



The series of cylindrically arranged collateral bundles inclosing the large medulla 

 and forming the xylem zone or woody cylinder has already been illustrated in the 

 description of the cortical region. It is typically cycadean, and its development as 

 a simple zone, as seen in trunk 393, is quite characteristic of all the fossil cycads 

 studied by the writer, with the notable exception of C. Jenneyana and C. ingens, 

 described below. 



In trunk 393 the collateral bundles or "woody wedges" form the usual typical 

 cylindrical trellis, from the lower angles of the openings or meshes of which the leaf 

 and peduncle traces arise, as already shown in macroscopic detail in figures 36-38. 

 Each bundle of the cylinder is composed of the inner xylem and outer phloem in 

 about equal areas, separated by a narrow line of crushed or imperfectly preserved 

 cambium. The cells of the xylem are quite equally heavy-walled throughout, as 

 shown in the several figures, although it may be that in these accompanying figures 

 the walls are shown relatively too heavy. (See also the photographs of the same 



