﻿CHAPTER IX. 

 EXISTING AND FOSSIL CYCADS COMPARED. 



It has already been shown in the several preceding chapters that the main 

 differences between the vegetative features of existing cycads and the Cycadeoidese 

 consist in structural modifications in the cortex held to be of comparatively recent 

 origin. And even were there no further analogies to judge from, the universally 

 simpler structural type of all the extinct eyeadaceous trunks thus far discovered 

 would alone make such a fact probable. On the other hand, comparison between 

 the types of fructification exhibited by the two groups can only be made in terms 

 of much changed features, for the greater part separated by wide intervals of time. 

 Before attempting the more formal consideration of the complex relationships 

 involved, it is therefore a method of convenience, if not a necessity, to place in 

 connected review the main facts concerning the distribution and organization of 

 the Cycadacese, with especial reference to those details of the greater interest and 

 value in making extended comparison with the Cycadeoidese. 



THE CYCADACE/E. 

 DISTRIBUTION. 



The existing Cycadacese form an ornate and compact group of gymnosperms, 

 including nine genera and 107 enumerated species indigenous to tropical and 

 subtropical regions (68). Of the genera, four — Zamia, Ccratozamia, Dion, and 

 Microcycas — are natives of the New World. The other five — Cycas, Macrozamia, 

 Stangeria, Encephalartos, and Bmvenia — are the Old World forms. Mexico, with 

 Ccratozamia, Dion, and many species of Zamia ; Africa, with Encephalartos and 

 Stangeria ; and Australo-Malaysia, with various species of Cycas, Macrozamia, and 

 Botvenia, represent the New and Old World regions in which cycadean vegetation 

 is most markedly developed. 



Occasionally cycads are abundant in particular localities. Thus Stangeria 

 paradoxa, one of the smaller species, forms thickets on the Natal border, and in 

 southeastern Australia considerable areas are closely set with Macrozamia spiralis. 

 As a whole, however, the existing cycads, in genera, variety of species, and prob- 

 able relative abundance as forest plants, play but an inconspicuous role as compared 

 with that plainly indicated by the fossil record for the eyeadaceous forms of Upper 

 Jurassic and Lower Cretaceous time. 



The most of the cycads are, for trunk-forming plants, low and inconspicuous, 

 the extremes in size lying between the dwarf Zamias with underground stems and 



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