No. 466.] STUDIES ON PLANT CELL. VIII. 721 



port my general program of sporogenesis with the free fibrillar 

 type of spindle formation. There seems to be little question 

 but that centrospheres are present and conspicuous in the early 

 mitoses within the spore of Pellia. They have been especially 

 studied by Farmer and Reeves ('94), Davis (:oi), Chamberlain 

 (:O3), and Gregoire and Berghs (:O4). All of these authors 

 have agreed that asters are clearly defined in the early mitoses 

 within the spore and most of them have termed the region of 

 kinoplasm in the center of the aster a centrosphere. The struc- 

 tures are less prominent in the third mitosis and are perhaps 

 replaced in later periods of the gametophyte history by kino- 

 plasmic polar caps. Polar caps are characteristic of the mitoses 

 in the seta of Pellia (Davis, :oi). However, Van Hook has 

 described centrospheres with radiations at the poles of the 

 spindles of the archegoniophores of Marchantia, whose centers 

 sometimes contained centrosomes, and it is possible that the 

 centrosphere runs through a considerable period in the life his- 

 tory of liverworts. There is complete agreement that the cen- 

 trospheres when present arise de novo and independently of one 

 another during the prophase of mitosis and that they disappear at 

 telophase. Ikeno has, however, described centrosomes during 

 the mitoses within the antheridium which are said to divide and 

 pass to opposite sides of the nucleus where they become the 

 poles of the spindles. They cannot be found after the mitosis is 

 completed, but are described as formed de novo in the interior 

 of the nucleus and thrust through the nuclear membrane into 

 the cytoplasm previous to each mitosis. After the final divi- 

 sion in the antheridium, the centrosome remains to function 

 as a blepharoplast. 



Thus we see that the liverworts present during their life 

 history an almost complete range of kinoplasmic structures 

 associated with the nuclear divisions from centrosomes and cen- 

 trospheres to polar caps and that type of spindle formation 

 characterized by free fibrillae gathered into cones but entirely 

 independent of definitely organized centers. There is also pres- 

 ent the blepharoplast. I emphasized this range of kinoplasmic 

 structure in my paper on Pellia and it seemed to me one of the 

 most interesting features of the liverworts. In this paper 



