37i 
Physiology of the Saprolegniaceae. 
the vegetative appearance was excellent. The gemmae in these cultures 
often passed over into zoospore formation in great numbers. Their shape 
approximated furthermore closer to sporanges than to oogonial initials. 
M. Aphanomyces laevis was also obtained in pure culture from a single 
zoospore, but only a few cultures could be made at the time. 
General Discussion. 
The different phases of the investigation may be divided into the 
following headings : — 
I. Relation of growth and reproduction. 
II. The development of the sexual organs. 
III. Physiological varieties. 
IV. The problem of species. 
I. 
All the species studied above showed the same general reaction on the 
various substrata as Saprolegnia mixta. They all grew rapidly on beef- 
gelatine, meat, and pea-broth. There is, however, a decided difference in 
the rate of growth ; and on this point some observations were made with 
beef-gelatine cultures in Petrie dishes. Cultures of .S'. mixta (H), S. hypogyna 
(C), .S. mixta (F), of the three unknown species (I), (K), and (L), and of two 
species of Achlya , were made on beef-gelatine by inoculating the centre of 
the dishes with them. The cultures were started February 13, and on the 
19th (I), (K), and (L) had grown to the margin of the dishes, while (H) and 
(F) and the two Achlyas were just half way ; (C) had reached a point about 
half way between the other two lots. The dishes were all kept under the 
same conditions of temperature, &c. Other incidental observations had all 
along pointed to this result. This of course does not indicate the absolute 
rate of growth. Under favourable conditions of temperature and nutrition 
they grow to the margin in a very much shorter time. The few trials made 
indicate a rate of *2 mm. per minute, or even less than a minute. 
It is to be noted that the two rates of growth are correlative with the 
two sets of species as regards their tendency to produce reproductive 
organs. (I), (K), and (L) do not produce oogonia under the conditions 
found by Klebs for S. mixta , or under the same conditions as found by 
myself for S. hypogyna and (H) and (F). This indicates a close physiological 
relationship between these latter species. It is quite clear that (I), (K), and 
(L) are different species, and if they are Saprolegnias, that they are possibly 
of close relationship among themselves. On the other hand (H), (F), and 
(C) seem to be also closely related physiologically, and a study of the 
nutrition relations of other species like S. monoica , S. ferax, and S. torulosa 
may show that these, too, act like 5. mixta ; such results would give us not 
only a morphological but also a physiological basis for classing them 
