Cytology of a new variety of A chly a americana . 145 
The normal course of development, as outlined above, is 
not often adhered to. The conditions are seldom so favourable 
as to admit of the life history being completed in so short 
a period as thirteen days. In cultures four months old, for 
example, a number of the oospores may be found in the 
resting condition. In cultures six months old I have generally 
found nothing but the empty cases of the oospores. The 
external conditions which determine the germination of the 
oospores are no doubt checked and controlled by internal 
conditions ; for, in oogonia on the same hyphae, in oospores 
in the same oogonium, even when kept in the same moist 
chamber in a single drop of water, noteworthy differences 
are almost constantly to be observed. I have seen in the 
same drop of water, in oogonia borne on a single hypha, 
kept under regular observation for several weeks, the following 
differences: — (1) The oospore germinates and produces a 
germ-tube which, instead of producing a sporangium, develops 
a small mycelium, as in Fig. 28, the branches of which are 
very delicate and of rhizoid-like character ; (2) the oospore 
germinates and produces one or more germ-tubes, which 
terminate in small sporangia ; (3) the oospore germinates, 
but fails to produce a germ-tube, and ultimately perishes ; 
(4) the oospore germinates and produces a germ-tube, but 
fails to produce sporangia, and ultimately perishes ; (5) the 
oospore germinates and ultimately produces sporangia, but 
the process of germination is effected in stages, with long 
pauses between, and thus sometimes extends over many 
days ; and (6) the oospore may remain in the resting con- 
dition. As the external conditions could scarcely be more 
uniform than they are in a small drop of water in a moist 
chamber, much of this variability must be due apparently 
to differences in the constitution of the oospores themselves. 
As it was of importance to me to secure cultures with large 
numbers of oospores undergoing germination at the same 
time, an endeavour was made to determine, to some extent, 
at least, the external conditions which were favourable to this 
process. In consequence of a verbal communication from 
L 
