Nuclear Division in the Hepaticae. 475 
together, they are often united into a sort of reticular system 
by threads of protoplasm. 
As time goes on the nucleus becomes angular, each angle 
corresponding to a centrosphere, and then a quadripolar 
spindle of an exceedingly well-marked type is seen as the 
further result of this angular extension. The nuclear wall is 
not broken, although it becomes greatly pulled out beneath 
each centrosphere, and thus the quadripolar spindle is thus 
far a nuclear distortion. The cytoplasm meanwhile alters its 
appearance, and becomes vacuolated in a manner highly 
characteristic for this and subsequent periods. The centro- 
spheres later become more closely approximated in pairs, and 
although I have not seen the process of fusion it is certain 
that the first karyokinetic spindle is bipolar , and that a simul- 
taneous division of the nucleus into four daughter-nuclei does 
not take place here, as it does in Pallavicinia h This fact, 
taken together with the approximation of the centrospheres 
in pairs, seems to point clearly to the merging of the original 
four kinetic centres into two, and it is highly probable that 
the ultimate axis of the bipolar spindle comes to lie in the 
direction of the resultant of those forces which are operating 
within the cell, and of which the centrospheres and the 
radiations are the visible expression. The particular parts 
of the protoplasm which are involved in the production of 
the radiations is of a different character from the intervening 
mass. Although during life the radiations are by no means 
rigid structures, they become so after death, and I was able 
to observe in one cell, the side of which had been broken off 
in cutting it, that the radii extended, unbroken, as stiff pro- 
jections beyond the edge of the fractured cytoplasm. 
Whilst the quadripolar protuberances of the nucleus have 
been in course of formation, the linin framework also under- 
goes further change. Chromatin begins to form abundantly 
within it, and especially so at the places where the thread- 
anastomoses are found. In fact ultimately it all is found 
localized in these spots, the linin shrinking up to them. 
1 Studies in Hepaticae. Annals of Botany, Vol. viii. 
