Baird—History of Phycomyces Nitens (Agardh) Kunze. 369 
the actively growing vegetative mycelinnij until the zygospore is 
mature. Then the nuclei^ acting as metabolic centers, proceed to 
transform available food into a reserve form of protoplasm which 
is stored in the space previously occupied by the vacuolar sap of 
the associated vacuole. As for the fat, I am unable to conclude 
whether it is a metabolic product of the cytoplasm or of the nuclei. 
In preparations of zygospores in which the protoplasm is' in a 
resting condition, the proportion of stainable substances and of the 
spaces appearing as vacuoles varies considerably. This variation 
is undoubtedly due to a difference in the amount of nutrition avail¬ 
able for the given zygospores. In some zygospores a comparatively 
large proportion of the space may be unoccupied by the deeply- 
stainable substances (fig. 7). In others the same substances occupy 
a much greater proportion of the space within the zygospores. In 
some cases this material is located largely in the peripheral zone, 
in others distributed more or less irregularly throughout. 
In crushing zygospores under water, bubbles always appear 
from within the rupture of the inner, leathery spore wall. There¬ 
fore, I conclude that the clear spaces appearing in preparations 
are in some instances occupied by gas resulting from metabolism. 
The protoplasts of zygospores five months old are unchanged in 
appearance from those that have matured up to the resting stage. 
After the zygospores are placed on moist agar for germination, one 
finds that many of the dense nuclear bodies become separated from 
each other by vacuolated cytoplasm. This change is most evident 
in the peripheral zone. In the more central region the nuclear 
structures stick together in large masses. In the peripheral zone 
there are many cases of a single nucleus with a vacuole or a group 
of several such nuclei surrounded by a very dense mass of slimy 
cytoplasm. The vacuoles associated with some of these nuclei have 
lost a large portion of their deep-staining substance. Figure 8 
illustrates a section of a germinated zygospore with a portion of 
the germ tube. It contains many of the nuclear structures filled 
with food reserve as has been described for the zygospores before 
germination; many of them persist during zygospore germination 
and the formation of the sporange. In the peripheral zone are 
many of the dense cytoplasmic masses surrounding one or more 
nuclei. Figure 8a shows such a cytoplasmic mass, wherein one 
nuclear structure is still unchanged, and from at least two of the 
nuclear vacuoles the reserve food has been dissolved. The later 
condition of the nuclear vacuoles is clearly illustrated in figures 
