﻿TRUNK STRUCTURE. 



75 



thin sections, plate XVI, i and 5.) The radial rows of xylem cells, as separated by 

 medullary rays from one to two cells in thickness, are from 30 to 60 in number in 

 each main bundle segment, and increase from a single cell in width, where abutting 

 on the medulla, to from two to five cells in width on the outer cambial side. The 

 medullary ray cells near the inner origin of the xylem rays are of very regular, 

 somewhat flattened, oblong form, several times as long as broad, and lie with their 

 greatest length tangential to the trunk. Further out these cells are longer, and their 

 greatest length is in the radial direction. The xylem is composed mainly of scalari- 

 form tracheids. Spiral cells are present next to the medulla, but are not numerous. 

 Idioblasts are occasional. No pitted tracheids have been noted, although preserva- 

 tion is such as would presumably enable ready recognition without staining, were 

 such present in any of the several radial or tangential sections cut. They may, 



2. (o o. x 1 00. 



T. 393. S. 211 and 260. v |Q0. 



Fig. 41. — Cycadeoidea Wielandi Ward. 



c, Middle region of xylem cut transversely, showing distinctly hexagonal phenocryst patterns extending through 



the cell walls as secondary structures formed in a solid or plastic mass behaving as a solution. 



d. Abutment of a woody wedge on medulla as seen in transverse section. A nucleus-like, if not nuclear, body 



is present in nearly every medullar parenchyma cell. 



perhaps, appear in further sections in agreement with those observed by Lignier in 

 Cycadeoidea micromycla, in which the pittings on radial longitudinal surfaces are 

 cross-slitted, as are those of the tracheids of Araucaria hrasiliana and Cordaites New- 

 berryi. The xylem is both greater in quantity and markedly denser than in the 

 weakly developed woody cylinder of the Florida Zamias, and the predominance of 

 scalariform elements is quite in contrast to Z. floridana, where the main body of the 



