﻿EXISTING AND FOSSIL CYCAOS COMPARED. 



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have been described from megasporophylls that so nearly approach the structure 

 of the central concentric bundle of the cycadeoidean seed pedicels as does the basal 

 bundle of the somewhat leaf-like sterile sporophylls from the summit of the stam- 

 inate cone of Stangeria paradoxa (fig. 129, 1). This resemblance is quite complete 

 in both relative size and distribution of the xylem and phloem, but there is no 

 bundle sheath. Very similar, though still more reduced, bundles of this same 

 type occur in the peduncle of the ovulate cone of Ban 'enia. Hence the more distinct 

 concentric bundle from the staminate cone of Stangeria may with safety be used 

 in completing the series of bundles mainly derived from the megasporophylls of 



X'. 



Fig. 1 3 1 . — Cycas revoluta. Transverse section from stalk o( a carpel, showing same structure as in preceding 

 figure, and further illustrating the persistence of ancient structures in reproductive organs of cycads theoret- 

 ically due to reduction and the checking of further increase in diversity of form. To the left is a small inverted 

 cortical bundle comparable to those outside the main concentric bundle in figure 129, II. (From Scott.) 



the existing cycads, figured above and intended to show the range of structure 

 from the most complex to the most reduced of the concentric bundles. 



It is, of course, to the examples of concentric rather than collateral structure 

 we must look for indications of relationship with so pronounced a concentric form 

 as that of the cycadeoidean seed pedicel. Needless to say, however, in considering 

 the possibility of the evolution of a bundle like the latter from a hypothetical type 

 approximating the complexity of Cycas, it is permissible to go beyond the actual 

 changes indicated in the figure without transgressing the limits of evolution within 



