Davis . — Nuclear Studies on Pellia. 1 7 1 
pendently of one another, organized the spindles in the 
manner characteristic of Pteridophytes and Spermatophytes. 
In the second an aster with a centrosphere is developed during 
the prophase, but becomes less prominent at the metaphase, 
and disappears before the daughter-nuclei are formed. In the 
third phase the kinoplasm forms two caps fitting closely over 
the ends of the elongated nucleus, and these are changed into 
the poles of the spindle. Fibrillae, centrospheres, and the 
kinoplasmic caps, however they may be arranged, are all 
secondary developments from the primal granular protoplasm 
which is the only form of kinoplasm in any sense permanent 
in the cell. 
Arising from accumulations of granular kinoplasm during 
the prophase, the substance of the fibrillae, centrospheres, or 
caps returns to a similar condition at the completion of mitosis, 
or is lost in the general cytoplasm of the cell. We do not 
yet know the structure of the nuclear figures when sexual 
cells are organized, or during the later periods of the gameto- 
phyte’s history, but it is not unreasonable to expect a blepharo- 
plast at the time of spermatogenesis. However^ as nuclear 
division proceeds in the spore the centrosphere becomes less 
conspicuous until it cannot be distinguished, and the kinoplasm 
takes the form of a cap. It seems probable, therefore, that 
mitosis throughout most of the period of the gametophyte 
takes place, with spindles organized from caps of granular 
kinoplasm, as is the case in the seta. 
The bearing of these data on the probable evolution of 
mitotic phenomena in higher plants from conditions in the 
Thallophytes is most interesting. We cannot trace the centro- 
sphere or the aster phylogenetically back to the Thallophytes, 
for neither remains throughout the ontogeny of Pellia . We 
do not know the facts for the Algae most closely related 
to the Hepaticae (higher types of the Chlorophyceae, such as 
Coleochaete ), but even if it be found that these forms have 
centrospheres and asters we shall still have a puzzling problem 
before us. For a connexion between such structures and the 
conditions in the Hepaticae may only be followed through 
