﻿2 2S RELATIONSHIPS. 



columnar forms, and also include the much different slender and freely branching 

 . inomozamites. The fossil group as now known hence presents by far the greater 

 diversity of trunk forms. 



In brief, there is not a single vegetative character of the Cycadeoidece which 

 does not find a near analogy in the existing forms, and such minor differences 

 as are present in the latter readily explain themselves when separation in time is 

 considered. Moreover, three pertinent correlative questions arise in this connec- 

 tion, and their probable answers can not be thrust aside if we wish to properly 

 adjudge the significance of all the facts. 



Firstly, what would the vegetative parallelism and agreement have been could 

 the Cretaceous ancestry of the existing cycads be compared in microscopic detail 

 with all the coexisting fossil forms; that is, with that more inclusive cycadalean 

 group, of whose members surely all can not yet be known ? Probably complexity 

 of leaf traces in the line leading into the modern cycads would have been the only 

 difference that had yet arisen in advance of the more ancient vegetative features 

 of the Cycadeoideau. 



Secondly, could such a comparison as that just indicated have been made in 

 early Triassic time, when Anomozamites, the oldest cycadeoideau form known with 

 certainty, flourished ; what macroscopic or microscopic feature would have been 

 present in the one group and wholly absent from the other ? Probably none. 

 Moreover, after comparison of many forms, it must be held as strange indeed if 

 at that time genera did not exist so combining the characters of both the groups 

 as then developed as to have made it difficult to define an intervening border line, 

 if indeed such existed at all, so far as vegetative features are concerned. 



Thirdly, could the far-reaching identity and similarity in the vegetative struc- 

 tures of the two cycadean groups be the homoplastic result of physiologic condi- 

 tions of growth and evolution alone, and merely the result of parallel development 

 from two distinctly and remotely separated fern groups ? Probably not. The reason- 

 able hypothesis is that the ancestral line from which the cycadeoideau and exist- 

 ing cycads sprang remained single and homogeneous until the major outlines of 

 leaf and stem similarity now common to the two groups were established. That 

 this original stem type had peculiarities now obscured is of course obvious enough. 

 Probably its greatest departure from the various known Jurassic and Cretaceous 

 trunks lay in the possession of a woody cylinder of mesarch bundles, and a much 

 more prominently concentric type of cortical bundle. 



COMPARISON OF REPRODUCTIVE CHARACTERS. 



The lateral bract-inclosed cones of the monopodial stem of the Cycadeoideau, 

 as already remarked, are analogous in position and general form to the scale-leaf 

 buds of old trunks of Cycas. Also, according to our view this analogy goes much 

 farther than mere outward form and position. For we regard the bracts of the 

 cycadeoideau strobili as homologous to foliage leaves, scale leaves, and sporophylls, 

 just as in the existing cycads there is a primitive identity in the leaves, scale leaves, 

 and sporophylls of the cones of both sexes. In the earlier growth stages of the 



