Graham. — Nuclear Division of Preissia commutata. 669 
the first mitosis (a division that has not been studied) they disappear entirely 
by the time the thallus is formed. Farmer and Reeves (’94), in their study 
of the germinating spores of Pellia epiphylla , believe that the elongation of 
the nucleus in the early prophase is due to the influence of the centrospheres. 
If there is some controlling force at the poles of the nucleus which causes 
it to elongate, it is certainly not to be ascribed in ail cases to demonstrable 
centrospheres, for they are not present in the somatic cells of Preissia 
commutata , where the elongation of the nucleus is marked. Van Hook (’00) 
does not attempt to explain the elongation of the nucleus in cells in 
the stalk of the archegoniophore of M archantia polymorpha ; nor does 
Chamberlain (’03), who found that the nucleus in Pellia epiphylla elongated 
after the spireme had become segmented into chromosomes. Nemec (’99) 
believes that some force acts on the nuclei of cells in Seed Plants which 
tends to pull the nuclear wall in the direction of the force. By chloroforming 
or plasmolysing the living tissue the nuclei become spherical. 
The formation of the spindle fibres in Preissia commutata follows the 
method of their formation in many other forms, and shows that the process 
in this plant is similar to that in the seed plants. Upon the elongation of 
the nucleus the granular masses of cytoplasm at the ends of the nuclei are 
conspicuous. When the triple stain is used, the granules take the aniline- 
saffranin stain. The appearance of the kinoplasmic caps are described in 
the vegetative cells of a Liverwort (. Pellia epiphylla) by Davis (’01), and his 
illustrations show that this cap is composed of granular cytoplasm. Farmer 
and Reeves (’94) state that the achromatic spindle develops from the cyto- 
plasmic radiations of the centrospheres in the germinating spores of Pellia 
epiphylla . In M archantia polymorpha , according to Van Hook (’00), the 
radiations from the centrospheres meet to form a spindle, while Chamberlain 
(’03) believes that the spindle fibres in the germinating spores of Pellia 
epiphylla are formed from hyaline caps that become granular and then 
fibrous. 
The earliest prophase in Preissia commutata , in which the nucleus 
elongates and the chromatin substance increases materially, is similar to the 
same stage in the higher plants. This stage in higher plants has been 
described many times by many students. In a Liverwort it has been 
described by Van Hook (’00), and the results of my investigation agree 
with his, except that the centrospheres he finds at this stage are absent 
from the plant now under consideration. 
The results of this work show that from the earliest prophase to the 
reconstruction of the daughter nuclei, mitosis in the vegetative cells of the 
Liverworts agrees with that in the higher plants, as described by many 
investigators. 
