﻿104 VEGETATIVE FEATURES. 



fuse growth of ramentum, although the remnant of a once heavy growth is certainly 

 present. Proliferation of a simpler type is exhibited by the free production of 

 adventitious foliage leaves quite directly and with little or no lateral bud develop- 

 ment in such forms as Cycadcoidea ingens (trunk 208) and Cycadella ramentosa ; and 

 in this respect the parallel with existing forms is absolutely complete. 



The even color and rock-like outer surface of Cycadeoidea ingens (type) make 

 the precise disposition and number of the leaves forming its crown difficult to deter- 

 mine in the absence of large sections. Moreover, the large size of the trunk and 

 its excessive hardness and toughness — exceeding chalcedony in these respects — 

 would make such sections extremely difficult to cut ; but those above described 

 display the main features. It is, as stated, clear that several circumvolutions of 

 young fronds are emerging, and that interior and apical to these there is a heavy 

 crown of terminal ramentum at the base of which the fronds of another season of 

 growth may already be developing ; but owing to the far smaller size of the more 

 apical fronds it is not impossible that frond growth was more or less continuous 

 throughout the year, with partially emergent fronds nearly always present, in which 

 case such will be found on most well-preserved trunks of this species. Indeed it 

 might even be that while in the existing cycads continuous frond emergence is 

 rather rare, the reverse may have been true of the fossil forms. 



The relations of frond succession are clearer in another species, Cycadeoidea 

 colossaiis, as observed macroscopically and in the handsome transverse thin section 

 shown in figure 52. Here, as noted, there appears to be more or less of a hiatus 

 in growth between the series of partially emergent fronds and the ramentum areas 

 immediately succeeding them, these also being of about the same number as the 

 pinnule-bearing fronds. Hence we can not doubt that in many of these plants grow- 

 ing amidst the generalized tropical conditions of the Upper Jurassic as far to the north 

 as the Black Hills (44 N.), the wilting down of old leaves and the growth of new 

 crowns mainly proceeded with the seasons. The facts, therefore, as thus far corre- 

 lated and at present understood, do not indicate the rate of foliar and trunk growth 

 of the fossil to have been either more or less rapid than that of the existing cycads, 

 and as in the latter mainly dependent upon the leaf and scale-leaf succession. 



