﻿BISPORANGIATE AXES. 



161 



oue end, which may very well represent a large prothallial cell. In fact, the 

 presence of an indicated prothallial cell or tube cell is less open to question than 

 any of the other supposed cell markings here noted. In some other cases markings 

 are present which may indicate several cells, and sometimes more, as many as five. 

 If in such instances cells are indicated, rather than mere ruptures of the iutine or 

 extine, more numerous cells are present in this stage of pollinial development 

 than in existing gymnosperms, but not so many as in the case of Cordaites, 

 accepting the view that the markings seen in the pollen grains of that fossil 

 are truly prothallial. Certainly one may readily imagine the three distinct cells 

 to be seen alike in the mature pollen of Ginkgo and the living cycads — that is, 



Fig. 85. — Cycadeoidea dacotensis. Transverse section of bisporangiate strobilus. X 3. 



Specimen from nine miles northwest of Sundance, Wyoming. Cut just above the apex of the ovulate cone. Siliceous matrix in 

 solid black. At the center the outlines of the seventeen or eighteen decurved tips of the staminate fronds may be clearly seen, 

 and around these tips a zone of narrow and compressed synangia borne by them. The coloration in the fossil itself is light but 

 distinct, so that it was possible to trace this drawing showing the distribution of the synangia directly from an enlarged photograph 

 of the polished surface. 



the vegetative or prothallial, the generative, and the tube cells — as outlining them- 

 selves by markings not unlike those seen in the present fossil pollen, if similarly 

 fossilized. But on the other hand, such delicate cell walls may be better considered 

 as nearly always failing of preservation, and as only being marked in the case of 

 numerous pollen grains in a given specimen in exceptional cases. It is hence pos- 

 sible that some of the markings shown in outline, figure 84, represent cells, and 

 that some may be the result of chance is also likely. Plainly, however, if cells are 

 in part indicated, there were more than three, and prothallial elimination had not 

 proceeded so far as in the modern gymnosperms, but farther than in Cordaites. A 

 five-celled stage is the most probable (cf. the grain shown in photomicrograph 4, 

 plate xxxi). While, of course, it is not possible to homologize on the basis of such 

 meager evidence, the condition which would seem to be indicated is the one which 



