COMPARATIVE MORPHOLOGY OF GYMNOSPERMS 163 



Pteridophytes, although we recognize the fact that there may 

 be grounds for considering the generative cell as the antheridium 

 initial, in which case the structures can not be homologized with 

 those of the heterosporous Pteridophytes. This large cell di- 

 vides unequally, giving rise to a sterile tube cell (the larger), 

 which is concerned with the development of the pollen tube, and 

 a smaller primary spermatogenous cell or generative cell. The 

 spermatogenous series, beginning with the generative cell, seems 

 to be very uniform in Gymnosperm^, and is longer by one gen- 

 eration than is the series in Angiosperms. The generative cell 

 divides and forms the stalk and body cells, the former of which 

 functions no further. The body cell divides and organizes the 

 two functional male cells, the morphological equivalents of the 

 sperm mother cells of Pteridophytes. If the stalk cell, sister of 

 the body cell, should also divide,, four male cells would result, 

 and the sequence would be that of Isoetes. In the Cycads these 

 male cells become ciliated, through the very peculiar activities 

 of blepharoplasts, but they should not be regarded as the homo- 

 logues of the multiciliate sperms of Pteridophytes. Whether 

 the ciliated sperm of Giiikgo is the transformed mother cell or 

 not is a matter of doubt, for although the details of its forma- 

 tion seem to be identical with those of the ciliated male cells 

 of the Cycads, there is evidence that they are organized within 

 the mother cells and discharged, in which case they are the mor- 

 phological equivalents of the sperms of Pteridophytes. It is 

 barely possible that there is here a transition form between a 

 discharged ciliated sperm and a retained sperm resulting in a 

 ciliated mother cell. 



Some meager evidence as to the nature of the male gameto- 

 phyte of Cordaitales is very suggestive. Within the well-pre- 

 served pollen grains a mass of tissue has been observed, whose 

 nature, whether vegetative or antheridial, it is impossible to 

 determine. In either event it indicates a much more primitive 

 male gametophyte than has been found in any living Gymno- 

 sperm. The testimony from the structure of the male gameto- 

 phyte indicates an origin of Gymnosperms from forms whose 

 gametophytes had more complex vegetative tissue than is shown 

 by any living heterosporous Pteridophyte. 



