Keene—Studies in Zygospore Formation. 
1207 
apart from each other and round out. At this time, a large 
central vacuole becomes apparent in each and the cytoplasm 
at the point of contact of the two gametophores is very dense. 
This is evident in fresh material and is particularly well brought 
out in stained preparations (figs. 9 and 10). There are few, 
if any, small vacuoles and the nuclei are very closely placed. 
The time of dissolution of the contiguous walls varies here 
as in Sporodinia. Sometimes the gametes are cut off from the 
suspensors before the protoplasmic masses come into contact, 
but in other cases, the intervening wall is resorbed before the 
new delimiting walls are established. This condition has 
been checked carefully in living material. Figure 10 shows a 
section through the gametophores before the formation of the 
cross walls. This formation, however, is a matter of a very 
short space of time, both being accomplished within an hour. 
The formation of the delimiting walls proceeds as it does in 
Sporodinia. The new wall forms first at the surface and closes 
in gradually in the form of a diaphragm which finally severs 
the intervening strand of protoplasm. The same papilla-like 
structures found in Sporodinia characterize these walls. 
The intervening wall separating the two gametes is usually 
dissolved first at the center but may be resorbed in several 
places at once. (fig. 10). The protoplasm of one gamete 
pushes its way into the protoplasm of the other. Here again, 
as in Sporodinia , the author is not inclined to ascribe any sig¬ 
nificance to this act as due to a sexual differentiation. It ap¬ 
pears rather to occur as the result of turgescence. If the in¬ 
ternal pressures are not at an equilibrium, which is hardly to 
be expected, when the wall weakens at one spot, the gamete 
/ possessing the greater osmotic pressure is released and surges 
into the other. Ultimately, the separating wall disappears and 
the two gametes appear as one mass (fig. 11). Occasionally 
fragments of this wall may be discerned in the zygospore. 
An interesting and somewhat perplexing condition arises in 
the appearance of the nuclei at this time. As the young zygo¬ 
spore is delimited and the protoplasm of the two gametes be¬ 
gins to mix, there occurs a characteristic grouping of the nuclei. 
There appear to be from twelve to sixteen nuclei aggregated 
in a group (fig. 11). It is impossible to state with certainty 
that in each group there are nuclei from each gamete, as there 
