264 BOTANICAL GAZETTE [march 



forms (cycads) this fragmentation becomes a very much modified 

 process, may be a manifestation of the power of division which is 

 one of the chief characteristics of centrosomes. According to this 

 interpretation the first fission of the blepharoplast of Blasia (fig. 10) 

 would correspond to the centrosome division which would normally 

 occur if another mitosis were to take place, and the further frag- 

 mentation would represent a further manifestation of the cen- 

 trosome' s power of division which may have been retained from 

 a time when more spermatozoids were produced from a mother 

 cell, and which has in some way become a feature of the develop- 

 ment of the cilia-bearing structures. In this way Blasia may shed 

 light upon the origin of the remarkable behavior of the cycad 

 blepharoplasts. 



To this idea, which presents itself as a suggestion and may 

 scarcely deserve to be proposed as a theory, there are obviously 

 many objections. Chief among these is the fact that fragmenta- 

 tion is most conspicuous in the blepharoplasts of the cycads, but 

 developed almost not at all in those of the bryophytes, which 

 would be expected to have retained in the manner of their elonga- 

 tion more evidences of a derivation from normal centrosome 

 division. It is possible, however, that the simple fission of the 

 blepharoplast as seen in Blasia was soon replaced in most 

 bryophytes and pteridophytes by uniform elongation without 

 fragmentation through the failure of the fission to occur^ after 



>c> ***^* wv* «v« vxxx ^ ^ fe 



the slight elongation normally preceding it (figs. 7-9)? ^ 1S 

 elongation then continuing to form the uniform cilia-bearing 

 thread. Fragmentation would thus be a retained feature in 

 Blasia, Equisetum, Marsilia, and the cycads, although the manner 

 in which it is accomplished in the higher forms (through a 

 complex process of vacuolization rather than simple fission) 

 would still be regarded as an advanced feature subsequently 

 evolved. Whether, therefore, the objection stated rules out the 

 suggested explanation or not can scarcely be decided in view of 

 the fact that the evidence at hand has been obtained from so 

 few bryophytes and pteridophytes, comparatively speaking, and 

 especially in view of our lack of adequate knowledge of blepharo- 

 plast origin and behavior in the algae. 



