﻿EXISTING AND FOSSIL CYCADS COMPARED. 227 



COMPARISON OF VEGETATIVE CHARACTERS. 



In the pith of the cycadeoidean trunks no such caulinc bundles as are present 

 in some existing cyeads have been found, but layers of internal periderm are 

 met with in both groups, the relative development and other medullar characters 

 also being the same in both. In the primary woody cylinder of collateral bundles 

 agreement is complete, although it is not yet determined that the secondary thick- 

 ening described in Cycadeoidea (pages 78-80) is directly comparable to that of 

 various existing cycad trunks. 



In the cortex the same elements are presented in both groups, but the direct 

 course of the cycadeoidean leaf traces agrees only with that of sporophyll traces of 

 the cones of recent cyeads, the complex anastomosing leaf-trace system of the latter 

 being of variable development, not always present in young plants, and clearly a 

 condition acquired since the segregation of cones, also since the cycadeoidean and 

 cycadean lines separated. 



In the leaf bases the same general characters occur, but instead of the more 

 recent omega bundle pattern there is constantly present in the fossil forms a 

 more fern-like V-shaped grouping, occasionally further modified. The cylindric 

 disposition of the leaf-base bundles in Stangeria and Bowenia is, however, of inter- 

 mediate type. 



Scale leaves have not yet been structurally determined in the American Cyca- 

 deoidese, but doubtless occurred sparingly, similarity to existing cyeads in this 

 respect probably going further than mere agreement with such Macrozamia species 

 as bear only fully developed foliage leaves. Moreover, Seward distinctly states that 

 a Paris Museum specimen of // HUiamsonia bears along with more or less detached 

 fronds " typical WUliamsonia scale leaves " (145). 



In their ramental growth the cyeads have been seen to vary greatly, that 

 of the fossil forms being uniformly profuse and fern-like, that of the existing types 

 pauciform and vestigial. It has, however, been shown that this difference has arisen 

 through progressive reduction and can not be regarded as fundamental, since there 

 must have been a time when the development of rameutum was much the same in 

 both cycad groups. 



Prcfoliation of the fossil forms as observed in various species, including two, if 

 not three, genera was direct, as in Macrozamia and various other existing cyeads. 

 But the once-deflexed or semi-cireinate rachis of the microsporophylls or staminate 

 fronds of Cycadeoidea finds a further analogy in the similarly deflexed foliar rachis 

 of Zamia. Circinate pinnules have not been observed in the fossil condition, but 

 must have occurred. In leafy habit the two groups agree in all fundamental char- 

 acters, the pinnule form in both varying much within the same limits and the finer 

 details of structure being nearly the same. In their branching habits both cyca- 

 dean lines were much alike. Moreover, the scale-leaf buds of Cycas, which readily 

 develop into growing trunks, form a fundamental analogy to the laterally-borne 

 young branches and cones of Cycadeoidea and Cycadella. 



The cycadeoidean trunk types, while generally of lesser height than those of 

 the existing cyeads, present the same gradations from tuberous to branching and 



