F. Cavers. 
278 
sort formed by division.— Synchytriacece. b. Mycelium present. 
I. Mycelium of delicate evanescent strands, i. Mycelium related 
to a single sporangium.— Rhizidiacece. ii. Mycelium widespread, 
with both intercalary and terminal sporangia.— Cladochytriaccce. 
II. Mycelium of well-developed hyphae.— Hyphochytriacece. B. 
Sexual spore formed by conjugation of contents of two sporangia 
(gametangia).— Oochytriciccce. 
We prefer to join the Chytridineae and Ancylistineae as two 
divisions of one group, the Chytridiales. Schroter divides the 
Ancylistineae into two families, the Lagenidiacece in which there is 
no definite mycelium and the whole body is divided into either 
sporangia or sexual cells, and the Ancylistacece in which a vegetative 
mycelium-like portion remains over after the sporangia and sexual 
organs have been formed. We shall now deal with the families of 
Chytridiales, with special reference to what appear to be the more 
important bearings of recent work on their inter-relationships. 
In the Olpidiaceee the fructification is intracellular and 
spherical or ellipsoid, rarely ( Eetrogella) elongated, undivided until 
ripe, and produces either a thin-walled zoosporangium or a thick- 
walled resting sporangium. The simplest genera, like Reessia and 
Monochytrium, are distinguished by the actively amoeboid character 
of the naked parasite formed by the entering zoospore. Fisch 
(1884) described the amoeboid body of Reessia as moving about 
within the host-cell for a week or more by means of pseudopodia, 
and then giving rise to a zoosporangium the contents of which soon 
divided into numerous uniciliate zoogametes; these when set free 
united in pairs and the zygote settled upon and emptied its contents 
into an epidermis cell of the host ( Lemna ), there producing a thick- 
walled resting sporangium. Griggs (1910) described a new and 
apparently very closely related genus Monochytrium ; his account is 
less complete so far as the life cycle is concerned, but more detailed 
cytologically. Here again the entering zoospores become amoeboid 
and while some of them give rise to zoosporangia by division of the 
nucleus into four (meiosis?) followed after a rather extended period 
by repeated division of these four nuclei to form the zoospores, 
other amoebae fuse together (though their nuclei remain distinct) 
within the host-cell and the amoeboid zygote grows to form a thick- 
walled binucleate cyst whose further development and germination 
were not observed. 
In the remaining genera of Olpidiaceae (Fig. 6, A-E)the general 
course of the life cycle shows certain common features. The 
zoospores (either uniciliate or biciliate, in the latter case with one 
cilium directed backwards though both usually arise from the same 
point) have two motile stages separated by a brief period of rest, 
suggesting a primitive type of the biplanetism which is a marked 
feature of the zoospores of Saprolegniaceae and some Peronospor- 
aceae—this was found by Butler (1907) and by Barrett (1912) in 
various species of Olpidiopsis, etc. The young parasite formed 
within the host-cell by the entering zoospore is at first naked and in 
some cases for a time more or less amoeboid. In most cases there 
are two types of sporangium, thin-walled ones which quickly 
germinate and thick-walled resting sporangia, and in some cases the 
formation of the latter has been proved to be the result of a sexual 
process. I 11 most cases the sporangia, like the naked parasite from 
