igia] SHARP— SPERMATOGENESIS IN EQUISETUM 109 



centrosome 



cc 



rudiments" 



spermatogenous cells of Marsilia 



certain liverworts are so remarkably centrosome-like. Moreover, 

 many true centrosomes appear de novo in each successive cell genera- 



mitosis 



elimi 



from 



retained, if at all, in different degrees in different plants, and in those 

 cells in which it performs an important biological function, as 

 other workers have suggested. Webber's statement that no known 

 plant centrosome has the function of bearing cilia is no longer 

 without a possible exception, since Jahn (56) has seen the flagellum 

 of the swarmer of Stemonitis growing out from the centrosome 

 during mitosis, exactly paralleling what Henneguy (44) observed 

 in an insect. That the bearing of cilia is the function which is 

 to be held accountable for the retention of the centrosome in 

 spermatogenous cells seems highly probable. After having lost 

 the usual functions of a centrosome we might well find it appearing 

 still later, in the spermatid itself, as Woodburn (95) believes it 

 does in certain liverworts. Belajeff's view concerning the pres- 

 ence of these structures only in the spermatogenous cells is that 

 every cell has its definite "dynamic center," butonly in these cases 

 is a staining substance present. 



That growth into a band or thread does not deny the centrosome 

 nature of an organ is shown by the great bodily elongation of the 

 inner centrosome in the spermatozoon of Helix (Korff 58) and 

 certain elasmobranchs (Suzuki 82, Moore 68). The rodlike 

 centrosome of Dictyota and the discoid one of certain ascomycetes 

 constitute a further argument against allowing the character of 

 shape to enter into the definition of the centrosome. 



Thus from the standpoint of the theory stated in the foregoing 

 pages, the occurrence of secondary peculiarities developed in con- 

 nection with cilia-bearing in the cycads and certain pteridophytes, 

 such as large size, fragmentation, and growth into a band, does 

 not distinguish the blepharoplast from the centrosome. This is 

 emphasized by the fact that the first two of these features do not 

 occur in the blepharoplasts of bryophytes and most pteridophytes, 



