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 (:01), Chamberlain 
(:03), and Grégoire and Berghs (:04). 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, :01). 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 fibrille 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 
