Nos. 4SI4S2.] STUDIES ON THE PLANT CELL. 5 85 



of the blepharoplastoids of Shaw which as just described are 

 regarded by the latter author as centrosomes. Both Belajeff and 

 Ikeno are incHned to use the term centrosome with a looseness 

 that is unusual since the first accounts of this structure gave to 

 it a place in the cell which is not strictly followed in these 

 authors' descriptions of spermatogenesis. Ikeno's account of 

 the intranuclear origin of the centrosome is extraordinary. 

 Intranuclear centrosomes have been reported in several animal 

 forms but they do not leave the nucleus in the manner described 

 by Ikeno. 



On the whole the writer is more in sympathy with the views 

 of Webber (:oi,pp. 70 to 81), Strasburger and Shaw than 

 those of the other authors. Assuming that the observations 

 upon the cycads and Ginko are correct, Webber is certainly 

 , justified in emphasizing the striking fact that the blepharoplasts 

 are completely independent of the spindle in the body cell and 

 that they are formed de novo at a distance from its nucleus. 

 These are peculiarities which, if established generally through- 

 out spermatogenesis in plants, will remove the processes entirely 

 from the activities of centrosomes in certain thallophytes {e. g. 

 Stypocaulon, Dictyota) and in many animal cells. It is certainly 

 to be expected that a centrosome when present will always hold 

 an intimate relation to spindle formation during mitosis. It need 

 not be a permanent organ in cell genesis and an ever increasing 

 number of investigations indicate that it frequently is not. 

 Therefore many authors hold that the centrosome is rather the 

 morphological expression of a dynamic center than a protoplas- 

 mic structure with an individuality comparable to the organs of 

 a cell. But these universal characteristics of centrosomes are 

 apparently not present in the blepharoplasts of the gymnosperms 

 nor, according to Shaw, in the pteridophytes (Marsilia). But 

 then the observations of Belajeff and Ikeno are not in accord 

 with those of Shaw and it is possible that studies in zoospore 

 formation and gametogenesis among the thallophytes may pre- 

 sent the subject in new lights. 



For as shown in our discussion of the zoospore it is not clear 

 whether the blepharoplasts in those cells are always derived 

 in the same manner. We have Strasburger's view that the 



