304 
F. Cavers. 
oogonium, F. Sorolpidium beta: 1, cell of host showing amoebae in various 
stages of growth and nuclear division ; 2, young sorus showing nuclear division 
in the sporangia ; 3, part of same more highly magnified ; 4, a single sporan¬ 
gium of a sorus, showing nuclear division. A and F from Nemec ; 13 and D 
from Zopf ; E from Barrett. 
perhaps from Synchytrium mainly in having biciliate zoospores, 
while Micromyces has a spiny-coated sorus and appears to differ 
from Rozella mainly in having uniciliate zoospores. 
The life history and cytology of Synchytrium have been described 
by various writers, and a monograph of the genus has recently 
been published by Tobler (1913), so that in many respects it is the 
best known member of the Chytridiales. The parasite may produce 
either thin-walled summer sori or thick-walled cysts which remain 
uninucleate through winter and in spring germinate to form a sorus. 
In the latter case the division does not occur in situ but after the 
contents covered by the thin inner coat have burst through the 
outer coat. In 5. taraxaci the cyst divides directly to form zoospores, 
but in other cases the cleavage which accompanies nuclear division 
results in the formation of a number (30 to about 250) of sporangia, 
each of which divides into numerous uniciliate spores. The 
cytology of Synchytrium presents some remarkable features, though 
there is considerable diversity in the various species investigated, 
as well as some discrepancy between the accounts given by different 
writers for the same species. Thus in 5. taraxaci the primary 
nucleus divides by an amitotic process which may be termed nuclear 
gemmation, masses of chromatin (chromidia) derived from the 
nucleolus passing into the cytoplasm and becoming organised to 
form the secondary nuclei, which later divide by mitosis. In S. 
endobioticum this process is carried still farther, for here the 
extruded chromidia do not even organise secondary nuclei but pass 
unchanged into the zoospores, the remains of the primary nucleus 
persisting unchanged in the centre. Some features in the cytology 
of Synchytrium appear to have their only parallel among the 
Protozoa, where chromidial extrusion plays an important part in 
the organisation of the nucleus, but a careful comparison of the 
various accounts given hardly supports the view adopted by some 
authors that Synchytrium is completely isolated from the remain¬ 
ing Chytridiales. According to Nemec, Sorolpidium and Synchytrium 
are too sharply separated cytologically to be placed in one family, 
the main difference being that in Sorolpidium the nucleolus of the 
vegetative nuclei persists and divides directly (though at the same 
time a spindle is organised as in a typical mitosis) instead of passing 
into the the cytoplasm and providing material for the formation of 
the chromosomes as in Synchytrium. A very similar process has 
been described for the Plasmodiophorales, and it may perhaps be 
regarded as intermediate between direct (amitotic) division or nuclear 
gemmation, as seen in some species of Synchytrium , and ordinary 
mitosis ; and in view of the diversity in modes of nuclear division 
found within the limits of the genus Synchytrium, as well as the fact 
that there are various reasons for regarding the Chytridiales and 
Plasmodiophorales as being closely related, the cytological 
phenomena observed in Sorolpidium and Synchytrium appear simply 
to indicate that the former genus may be taken as a primitive type 
of Synchytriaceae and as connecting this group with the 
Plasmodiophorales. 
(To be continued). 
