i9i 2] SHARP— SPERMATOGENESIS IN EQUISETUM 105 



(73) 



lie was not made out in these three forms. According to Sands 

 the discoid "central body" or centrosome of Microsphaera 

 divides with its aster to two which occupy the poles during karyo- 

 kinesis. In Humaria rutilans Miss Fraser (27) saw at first two 

 centrosomes lying near each other, each at the apex of a cone of 

 fibers and surrounded by a very faint aster. These 



mov 



and establish the spindle in the usual way. Centrosomes 



figured 



In 



raser and Welsford 



centrosomes and asters. The figu 

 that division of the centrosome occi 



centrosomes 



weakly developed asters in Pyronema. The origin of the spindle 

 is not shown. 



The first centrosome described in the liverworts was that of 

 Marchantia by Schottlander in 1893 (75)- According to this 

 observer the centrosome in the spermatogenous cells divides 

 during the anaphases of mitosis, so that each daughter nucleus 

 is accompanied by two. In the gametophytic cells certain minute 

 bodies with radiations at the poles of the elongated nucleus and 

 of the spindle are believed by Van Hook (86) to represent 

 centrosomes. 



Pellia has been the subject of four investigations dealing with 

 the centrosome. In 1894 Farmer and Reeves (23) gave an 

 account of mitosis in the germinating spore. They reported two 

 centrospheres at opposite sides of the nucleus with conspicuous 

 radiations but no true centrosomes. The centrospheres occupy 

 the spindle poles and disappear during the telophases of division. 

 Davis (20) studied the same mitoses and obtained similar results. 

 He states, however, that the centrospheres fade out somewhat 

 earlier. The account given by Chamberlain (14) agrees with 

 these in the essential features. The structures are very distinct 

 in the first mitosis but become less so in the succeeding ones. The 

 most recent work is that of Gregoire and Berghs (33). By using 

 improved methods these investigators have found that neither in 

 the resting cells nor during mitosis are there centrospheres or central 

 corpuscles. The centrospheres described by other writers are 



