232 
AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
rest, and after their second escape germinating by a germ tube. Oogonia 
globular, short-pyriform or pyriform-globular, with a more or less short 
hyphal base, produced at the ends of main hyphae in basipetal series, or 
mixed with the sporangia in a sporangial series, up to 6 in a series (as far as 
observed), persisting in series until or after maturity of oospores; their 
walls firm, soon becoming pale brown, with more or less scattered, distinct, 
small pits, sometimes numerous. Oospores centric, 1-3 in an oogonium, 
rarely 4 or 6, at maturity with a thick wall and a granular central sphere 
separated from the wall by a layer of uniform thickness; the spores measure 
16-22 yu. Antheridia and antheridial branches none or very rare. 
Two collections: in shallow water over peat-like organic remains, shore 
of First Sister Lake, Ann Arbor, Michigan, and in a pool of sphagnum near 
by. Taken November 23. Cultivated on the house-fly, Musca domestica, 
from single zoospores. 
This species has for its nearest relative Saprolegnia monilifera de 
Bary," from which it differs in that its oogonia are persistent in the series 
in which they are formed until after the maturity of the oospores and the 
breaking down of the supporting hyphae. The oogonial pits, although 
scattered, are distinct, while in Saprolegnia monilifera'' they are said to 
be few or none. In de Bary's species the most general mode of proliferation 
of the secondary sporangia is by the method found in the species of Sap- 
rolegnia, while in the present species they are formed for the most part by 
the cymose method, and for a considerable time during my observations of 
fly cultures I did not see the other arrangement, not indeed until the cultures 
became comparatively old. The appearance of the sporangia-bearing 
hyphae, and the mode of proliferation of successive secondary sporangia, 
can be seen by referring to figure 4, a-c (Plate XIII). This is the regular 
process on the house-fly in 30-40 cc. of water, varying only in minor details. 
The oospores in the oogonia are also less numerous than appears to be the 
case in de Bary's species, but the character may vary somewhat in this 
group, even on the same substratum — although within limits — by reason 
of slight differences in the vigor of the mycelium as a result of a larger 
immediate food supply. In Saprolegnia monilifera''' the oogonia are said 
to be produced in great abundance, and sporangial formation is reported 
to be almost completely ended when the oogonia begin to form. In Isoachlya 
toruloides, on the other hand, sporangia and oogonia are often formed at 
the same time, from the time oogonia begin to form until the age of the 
culture and the toxic condition of the water begin to produce an effect and 
chlamydospores appear instead. 
The zoosporangia develop in the usual manner, and spore formation 
as seen in a living culture indicated nothing unusual. When the zoospores 
are ready to escape, the papilla at the apex of the sporangium is dissolved 
and they swim out at a fairly rapid rate and slowly scatter to a short distance 
before rounding up. I have followed this procedure in normal cases. 
A typical case is as follows. The culture had been kept in a cool glass- 
