Davis.— Nuclear Studies on Pellia. 167 
plastids and the usual cytoplasm with its alveolar structure. 
This zone of granular protoplasm is probably kinoplasm, but 
it fails to show further morphological differentiation. The 
writer searched in vain for the aster or centrosome that might 
be expected to accompany these resting nuclei. 
As has been said, the asters are most conspicuous at the 
first mitosis in the spore. They are usually also prominent 
at the time of the second mitosis, but are not as large. 
Fig. 35 illustrates the appearance of these structures at the 
prophase of the second mitosis, when the amount of kino- 
plasm has been so much reduced that the asters would hardly 
be recognized were it not for the advantage of their positions. 
The condition here illustrated is rather exceptional for the 
second mitosis, as the appearance of the aster is generally 
more like Fig. 30, but it shows excellently the conditions that 
appear shortly, as nuclear division proceeds in the spore. 
As a rule, the aster disappears after the third mitosis. The 
nuclei decrease in size, becoming perhaps only one-third of 
their former diameter, and while this naturally makes the 
examination with respect to asters more difficult, nevertheless 
the conditions seem clear. The writer found no asters with the 
prophase of the later mitoses. The spindle seems to arise 
from an accumulation of kinoplasm that forms a cap over the 
end of the nucleus, a condition that will be described in greater 
detail in the account of mitosis in the stalk of the sporophyte. 
Certain facts concerning the behaviour of the chromosomes 
in the mitoses of the spore are worth noting. The increase 
in the amount of the chromatin after the division of the spore- 
mother-cell is conspicuous, and results in the appearance of 
a linin network with deeply stained granules distributed over 
it. After a synapsis the linin and chromatin material takes 
the form of a broad spirem-thread. Synapsis is a phenomenon 
appearing with great regularity in the writer’s preparations, 
not only before the first, but also before the second and later 
mitoses. It is difficult to think of it as an artifact when found 
in different phases of ontogeny side by side with other stages 
that seem well fixed. 
