﻿56 



VEGETATIVE FEATURES. 



of the latter, together with the extensive production of laterally borne fruits. Indeed 

 there is among all the fossil cycad trunks from North America scarcely a single 

 example of a completely excised armor. In many trunks the armorial zone is 

 very heavy. (See figure 19.) 



Owing to the much reduced and vestigial character of the ramentum in the 

 existing cycads, and the regular order in which the leaves, scale leaves, or carpel- 

 lary leaves appear, the only dis- 



turbance of the regularity of the 

 leaf-base spirals that can occur 

 must be due to the sparse ap- 

 pearance of the terminal cones, 

 or scale leaf buds like those of 

 Cycas. This is but slight, and 

 very few trunks indeed exhibit 

 any apparent disturbance in the 

 regularity of the frond base 

 spirals. 



Such is not the case in the 

 Cycadeoidese. Only young 

 trunks, or the occasional trunks 

 which have not come into fructi- 

 fication, exhibit apparent regu- 

 larity in their leaf-base spirals. 

 As the profuse ramentum per- 

 mitted free change in the position 

 of the leaf bases during the 

 emergence of numerous and large 

 laterally borne fructifications, in 

 full-grown trunks nearly all 

 traces of the earlier spiral 

 alignment are quite frequently 

 obscured. But the true spiral 

 order in which the fronds orig- 

 inally appeared cau nevertheless 

 always be determined, if all the 

 leaf bases of a considerable area 

 are carefully examined and plot- 





Fig. 25. — Cycadeoidea sp. T. 751. 



Tangential section through a fragment from a trunk about 35 cm. in 

 diameter, cutting obliquely through the armor and into the cortex 

 which appears on upper side of figure. Lower leaf bases cut 4 cm. 

 distal to cortex, the obliquity of the section compensating for upward 

 slant of the leaf bases, so that they are cut in about a true transverse 

 section. Ramentum not shown. Since the large peduncle above is 

 cut several centimeters nearer the cortex than the lower fruit, it is not 

 clear whether the latter, as at first appears, is younger or not. X f • 



The marked increase in the size of the transverse sections of the leaf bases, the 

 diminution in the quantity of the ramentum, and the increased regularity of the spirals 

 are noteworthy features disclosed by the more deeply cut sections of the armor. Were 

 the present and preceding sections cut by different observers from different trunks of 

 the same species and from different localities, any difference noted might without due 

 consideration be held of specific value ; or if the peduncles chanced to be poorly indi- 

 cated or silicified the differences taken together might well be held of generic value. 



ted. When this is done the exact 



amount of change can always be determined and the true original position of every 

 individual leaf base always made out. Where this proves at all difficult, several 

 sections cut at successively lower levels, as suggested by figures 18 to 29, and more 

 especially by figures 25 and 26, will make the order clear. 



As the insertion of the leaf bases on the cortex is approached, their area 

 becomes larger and the amount of intervening ramentum correspondingly less. 



