﻿202 RELATIONSHIPS. 



The radial traces or bundles (in Cyras revoluta), after taking their origin in the 

 xylem zone, at first pass outward through the cortical parenchyma in a radial and 

 upward course about equal to the height of a leaf-base insertion. In most cases, 

 however, a division into two girdle branches soon takes place, sometimes even at 

 the point of origin, and these branches usually give rise to still others, with more 

 or less lateral anastomosis with other traces, as well as with younger traces above 

 and older ones below. The complex network thus formed is then attached laterally 

 and vertically to the more distinct girdle leaf traces, each of which, after its radial 

 origin, takes a low, unwinding spiral course through the peripheral cortex in right 

 or left direction nearly as much as 180 and then turns sharply outward into a leaf 

 base. A pair of such girdles leading from opposite sides, and even possessing a 

 common radial origin and thus girdling the circumference of the entire xylem zone, 

 constitutes the bundle supply of each leaf base. In consequence of this arrange- 

 ment the two bundles of each leaf base pass successively the bundles of each other 

 leaf base in a cycle of leaf bases. Moreover, as the cycles of leaves of successive 

 years appear, there results a more or less distinct grouping into annular zones or 

 girdles, but with more or less lateral anastomosis of radial and girdle connections 

 throughout. Along their entire length the inner sides of the girdles are connected 

 with the xylem by numerous successive radial traces, while the outer sides or those 

 next the surface of the stem are many times inter-united by still other connecting 

 bundles. In addition a quite complex bundle anastomosis may join the two girdles 

 as they enter a leaf base, and this anastomosis may be further joined to the xylem 

 zone by direct radial traces or receive cortical bundles. Also, after the girdles begin 

 to split up in the leaf base they may still receive cortical or radial traces. The 

 strength of the girdle leaf traces increases from their origin to the point of division 

 in the leaf base. 



The general course of the cortical bundles of Dion edule is quite similar to 

 that of Cycas. The girdle leaf traces may, however, depending on the extent of 

 periderm excision, lie very near the surface of the trunk in this species; and those 

 which finally enter the scale leaves are scarcely half the size of those supplying the 

 foliage leaves. This difference occurs in very much lesser degree in Cycas, but 

 may be general. 



Finally, certain anomalous cortical strands of concentric structure have been 

 noted in Cycas media, Stangeria paradoxa, etc. And bundles passing out rather 

 directly from the xylem, and ranged arc-wise or forming an imperfect cylinder of 

 bundles, as seen in tangential section of the cortex, also occur in Macrozamia (205), 

 though it remains to study such anomalies in connection with the cortical course 

 of the peduncular bundles. All peduncular series of bundles must present certain 

 variations from those entering the leaf bases ; but a searching comparative study 

 of the leaf base, carpellary base, and peduncle bundle supply of all of the several 

 cycad genera has never been made. The manner in which a series of pedunc- 

 ular bundle cylinders comes to be embedded in the pith of cone-bearing stems of 

 Ceratozamia and Stangeria has already been mentioned. These series in the older 

 portions of the stem pass through the xylem, cross the cortex to the base of the 



