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AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
types of secondary sporangia were present, de Bary's native conservatism 
naturally induced him to attach it to one of the older genera. 
An addition to the species which have this anomalous character of two 
modes in the formation of secondary sporangia during a sexual reproduction, 
was made recently by Coker (I.e.). He referred his species to the genus 
Achlya, as ''A. paradoxa,'* and felt disinclined to erect for it a new genus, 
on the ground that the anomalous character in question establishes merely 
a ''narrow point of contact" and is not unlike similar intermediate species 
in Puccinia and Uromyces. While this is clearly the case, limitations to 
genera cannot go on indefinitely encircling more and more exceptions, else 
one of the main reasons for the building up of the scientific classification 
of plants becomes abortive. Furthermore, in a group of such a small 
number of species as the Saprolegniaceae, the case becomes very different, 
by lack of balance, from the case in the genera of rusts cited. It seems to 
me, then, that by the erection of the genus Isoachlya, a double objective is 
attained: the limitations of the old genera remain clearly defined, and the 
new genus takes a most natural place within the family of the Saprolegnia- 
ceae. 
Botanical Laboratory, 
University of Michigan 
LITERATURE 
The student is referred to the extensive bibliography by Klebs for the older papers* 
and to Weston for more recent work. 
Klebs, G. Zur Physiologie der Fortpflanzung einiger Pilze. II. Saprolegnia mixta. 
Jahrb. Wiss. Bot. 33: 513-593- 1899. 
Weston, W. H. Observations on an Achlya lacking sexual reproduction, Amer. Jour* 
Bot. 4: 354-366. 1917. 
EXPLANATION OF PLATES 
The higher magnification was obtained with Bausch and Lomb 15 X ocular and 3 mm. 
objective, the lower with 15 X ocular and 8 mm. objective. All are equally reduced. Fig- 
ures 1-9 are from cultures on sterilized house-flies, in 25-40 cc. conductivity water, from 
single zoospores; all cultures were free from other organisms, 
Plate XIII 
Fig. I. Sporangial initials of Isoachlya toruloiles on head of a fly, two days after 
inoculation. 
Fig, 2, a. Young hypha before swelling, h-h. Stages in the development and 
maturity of zoosporangia. 
Fig, 3, a~f. Escaping zoospores and form changes in the process of assuming the 
first resting stage, a. During first twenty minutes, h-e. Gradual changes during next 
thirty minutes. /, Completely rounded and at rest. No cilia are shown, since full data 
were not obtained, but they are doubtless two in number and lateral. 
Fig. 4, a-c. "Achlya" type of formation of secondary sporangia, after nine days. 
Fig, 5, a-e. Different types of oogonia, showing the normal variation in number of 
oospores as the fungus occurs on flies. After nine days. 
Fig. 6. "Saprolegnia" type of formation of secondary sporangia. The proliferation 
in the two empty sporangia would become the third in the series. After thirteen days. 
