﻿EXISTING AND FOSSIL CYCADS COMPARED. 



2 2 f 



Fig. 129. — Transverse section of concentric megaspore supply bundles of existing cycads, with yet simpler similar bundles 

 from the sporophylls. All form a series passing from a highly complex type of concentric bundle, as in Cycas, 

 to extremely simple forms. These bundles illustrate approximately the range of structural variation in the concen- 

 tric spore supply bundles in existing forms, and at the same time suggest the manner in which the single concentric 

 bundle of the cycadeoidean seed pedicels must have been derived by wholly similar simple reductions. (Compare 

 ihe Stangeria and Bowenia bundles with figure 59.) (Selected figures from Worsdell.) 



I. Stangeria paradoxa. 300. From barren sporophyll. III. EncephaJartos horridus. ■' 100. Bundle entering megasporangium. 



II. Cycas revoluta. X 65. Strand about to enter megasporangium. IV. Bowenia spectabilis. 450. From stalk of megasporophyll. 



x, xylem; ph. phloem; x'~, centrifugal xylem; x', centripetal xylem ; px, protoxylem ; tf, transfusion tissue; s, bundle sheath. 



