﻿222 RELATIONSHIPS. 



envelope bundles, so far as observed, occurs in Stangeria with eight outer and 

 eight inner flesh bundles. In the Paleozoic Lagenostoma, so distinctly cycadean in 

 structure, there are nine bundles in the inner or nucellar, and nine in the outer 

 envelope, so that radio-symmetric types of cycad-like seeds are at least very ancient. 



Structure of the megaspore bundle supply. — The character of the bundles 

 entering the megaspore is of fundamental importance to our conceptions of theoret- 

 ical reduction stages and sporophyll metamorphoses. As investigated by Worsdell 

 the very large bundle entering the megasporophyll of Cycas revoluta is of a highly 

 complex mesarch concentric structure with accessory strands accompanied by much 

 transfusion tissue, the whole being inclosed in a prominent bundle sheath. As 

 appears in fig. 129, 11, showingthe structure o one of the two main bundles entering 

 the seed base, the minor strands, distributed round more than half the periphery of 



x' 



\ 1 \ H V h f TT ! V-V^-^v^y 32f 



Fig. 130. —Stangeria paradoxa. Transverse section of vascular bundle from upper part of a staminate 

 peduncular bundle ring, showing well-developed centripetal xylem, abutting on the compressed protoxylem. 



x 102. 



x 1 , centripetal xylem; px, protoxylem; x"*, centrifugal xylem; ph, phloem; cb. cambium. (From Scott.) 



the main inner concentric portion, are inverted and embedded in a region of cells 

 with conspicuous nuclei and dense protoplasmic contents. Also, the transfusion 

 tissue so prominently developed on the outer side of the minor strands may occur 

 independently of them, thus suggesting that it could take over their function 

 entirely by separate development around the main bundle as a transfusion tissue 

 zone. 



Much simpler types of concentric bundles occur in the much-branched bundle 

 system supplying the seed base in Encephalartos horridus. No bundles, however 



