no BOTANICAL GAZETTE [august 



but begin to appear in other members of the latter group, combined 

 with earlier stages in all essential points centrosome-like. 



Both Webber and Strasburger have pointed out that the 

 blepharoplast, since it remains behind in the cytoplasm of the egg 

 and does not meet the female nucleus, is inactive in fertilization, 

 while in animals the centrosome brought into the egg by the 

 spermatozoon plays a very important role in fertilization and in the 

 first cleavage mitosis. They advance this as a further evidence 

 that the blepharoplast and the centrosome are not homologous. 

 We have seen that as the blepharoplast has become more and more 

 highly differentiated in relation to the bearing of cilia, it has gradu- 

 ally lost the characters which would serve to mark it as a centro- 

 some. The disappearance of activity during fertilization along 

 with the other usual centrosome functions would be expected, if, 

 indeed, the sperm centrosome of plants ever did take any active 

 part in this process. In Nephrodium (Yamanouchi 97) and 

 probably many other pteridophytes and bryophytes the entire 

 spermatozoid enters the egg nucleus, but it is highly improbable 

 that the presence of the blepharoplast in these cases is necessary 

 to fertilization. On the other hand, we cannot yet certainly 

 conclude that a structure is entirely passive in fertilization merely 

 because it does not reach the female nucleus or produce other 

 striking visible effects. In any case it should be remembered that 

 function is not that upon which we can base homology. 



In denying the identity of the blepharoplast and the centrosome 

 Strasburger (80) derives the blepharoplasts of bryophytes, 

 pteridophytes, and gymnosperms from the thickened Hautschicht 

 organs of algal swarm spores and gametes. This theory appears 

 to have the support of current conceptions of phylogeny, but it 

 leaves the remarkable behavior of the liverwort, Marsilia, and 

 Equisetum blepharoplasts to be accounted for. That the Haul- 

 schicht organ seen in algae should assume, during the course of 

 evolution, such centrosome-like characters, adding them at the 

 earlier end of its life history, seems more difficult of comprehension 

 than the theory stated in the foregoing pages — that the centrosome 

 has gradually taken on the cilia-bearing function. 



