FAULL: DEVELOPMENT OF ASCUS. 
89 
The early elongation of the nucleus is undoubtedly accompanied 
by growth. It may be that, in addition to this, there is a tension 
brought to bear on the nucleus, a tension that may have its origin 
outside of the spore altogether (pi. 8, figs. 29, 32). That the bot¬ 
tle- or beak-shape is the result of a pull on the nucleus is rather 
more obvious, for there is an elongation without an appreciable 
increase in volume. Nevertheless this bottle-shape might be 
brought about through other changes, such for instance as the trans¬ 
fer of the chromatin and nuclear sap to the distal end of the nucleus, 
and the consequent shrinking of the proximal end. If there be a 
pull, however, it is not strong enough to pull the centrosome away 
from the delimiting layer of protoplasm. Indeed the centrosome 
does not sever its connection with the periphery of the spore mass 
until after the plasma membrane of the spore is constructed. 
The formation of the plasma membrane of the spore is subsequent 
to that of the limiting layer of protoplasm already noted, although 
it may begin before the latter is completed. Figures 26 to 30 (pi. 
8) represent this membrane in various stages of growth. In figure 
26 (pi. 8), only one of the poles of the spore is covered while in 
figure 29 (pi. 8), the membrane is all but finished. Figure 33 (pi. 
8) is a polar view of about the stage represented in figure 29 (pi. 8). 
Concurrently with the formation of the plasma membrane of the 
spore, another is formed in contact with it. This second membrane 
lines the cavity in which the young spore lies. Both occupy the 
site of the limiting layer of protoplasm, and along this their line of 
development follows. The development of these membranes is pro¬ 
gressive, beginning at a point contiguous to the centrosome and con¬ 
tinuing until the opposite pole of the spore is reached. To just 
what extent the substance of the limitino- layer enters into the com- 
position of these membranes, it is rather difficult to say. Nor is it 
clear that' their formation is preceded by a change in the limiting 
layer. It is certain, however, that the membranes are separable and 
a cleavage between them can be observed under favorable circum¬ 
stances up to the limits of their construction. Observation is 
rendered especially easy in case there has been a slight shrinkage or 
inequality in fixation (pi. 8, figs. 29, 33). 
In regard to the relation between the plasma membranes and their 
precursor, the limiting layer, it is highly probable that the develop¬ 
ment of the former is preceded by a cleavage in the latter. They 
