224 
J. Ramsbottom, 
which is connected with the nucleus. When there is an insufficiency of 
fluid present, the zoospores fuse in pairs. “The process of conjugation 
is not different from that common in various algae. 1 ’ In development the 
nucleus grows from 4 or 5 jit until it may reach the enormous size 
of 50 to 60 ju in the largest zoosporangia (cf. Synchytrium). The 
primary nuclei have enormous nucleoli and peculiar masses of chromatin 
as in the case of S. decipiens. “In the first type of mitosis the spindle, 
which is usually unipolar at first, is formed from coarse acicular fibers 
that appear within the nuclear cavity; it has no connection with the 
nuclear membrane. The spirem is formed from that part of the 
chromatin which lies in the equatorial region, the rest being cast out; it 
is frequently entirely within the spindle. The second type of mitosis 
presents no unusual features. No centrosomes or true asters were seen_ 
The cytology of Rhodochytrium bears a strong resemblance to that of 
Synchytrium. These resemblances suggest that Synchytrium was derived 
from protococcoid anestors.’ 1 
Kusano (1912) has studied the life history and cytology of 01- 
pidium Viciae. “In the fungi, the copulation of motile isogametes has 
hitherto received no special attention.” Sorokin (1874) described the 
mycelial vegetative body as derived from the zygospore resulting from the 
zoospores in Tetrachytrium. Fisch (1884) observed the formation of 
the zygote by copulation of zoospores in Reesia and Chytridium Meso- 
carpi. Griggs (1910) working with Monochytrium states that the swarm 
spores perforate the cell wall and enter the cells where they present 
amoeboid forms within the protoplasm of the host. Some of these fuse 
in pairs, the nuclei remain distinct and the zygote forms a binucleate 
resting spore. Other swarm spores grow to from zoosporangia. 
In 0. Viciae the zoospores are colourless and possess a long 
posterior ciliuin. The swarming period depends largely upon the tempera¬ 
ture. The zoospores undergo an “amoeboid deformation" several times 
before coming to final rest, when they soon begin to encyst. Copulation 
of zoospores is quite usual. A motile zygote is formed which behaves 
differently according to conditions. No external difference can be observed 
between the fusing zoospores, “but from the fact that any two spores 
coming into contact are not always induced to fusion ... it appears 
highly probable that a certain internal differentiation is called forth in 
becoming the gamete”. Kusano thinks there is “no attracting action 
between the zoospores” but that there is a certain period or age at which 
copulation is possible. “It will be seen that the sexual action ... is at 
an exceedingly primitive state and in reality a sexual distinction between 
the gametes is still obscure." After encysting, the zoospore and the 
zygote present a quite similar phase of development up to a certain stage: 
the former later develops into the zoosporangium, the latter into the 
resting sporangium. The mode of infection of the host plant is of the 
usual type. When the zoosporangium is approaching its maximum growth 
a membrane appears on its surface. At first it is uninucleate but with 
growth the nuclei increase in number. While the nuclei are few the 
cytoplasm is compact, then it becomes vacuolate and later reticulate. 
At this stage the nuclei become larger presenting a distinct structureslet, 
a nucleolus, chromatin and a few linin threads being recognisable within a 
well defined wall. In certain Phycomycetes this period is considered to 
