213 
Species of Olpidiopsis , (Cornu) Fischer . 
be distinct. The species found on Aphanoniyces is considered new and 
is given the name O. luxurians, while the other occurring on Saprolegnia 
is believed to be Cornu’s species O. Saprolegniae. 
These organisms appeared in water cultures prepared for the purpose 
of obtaining terricolons and aquatic Phycomycetes. Water from streams 
and pools containing Algae, dead twigs, and debris of various kinds, was 
placed in small glass vessels in fresh water. When soils were used, about 
one half-inch was placed in the bottom of the vessel and covered with 
tap-water one-half to one inch above the soil. The vessels used were 
provided with glass covers, and measured four inches in diameter and 
two and a half inches in depth. As traps, various vegetable and animal 
tissues were tried, such as sections of boiled root of Abutilon> suggested by 
Butler (4), sterilized flies, millipedes, Dipterous larvae, the larvae and pupae 
of ants, aphids, boiled egg albumen, &c. Although all of these, with the 
exception of the Abutilon root and egg albumen, proved to be more or less 
serviceable, the sterilized flies, aphids, and ant pupae were more extensively 
used. Ant pupae and larvae served best when cytological studies were 
made. 
Usually in cultures of this nature the most frequent forms secured are 
species of Saprolegnia and Achlya . In my cultures, however, Aphano- 
myces laevis proved to be more common than Achlya species, and was 
very commonly associated with some species of Saprolegnia . When any 
Chytridiaceous parasites were present, particularly on Saprolegnia , they 
could be seen with the naked eye within a few days after the culture had 
been started. Their presence is detected by the bright whitish specks seen 
among the radiating hyphae of the host (PI. XXVI, Fig. 75). These specks 
are the swollen hyphae with the enclosed developing parasite. 
When the parasite was once located by means of small scissors, the 
filaments containing it were cut off under a dissecting lens, washed in 
sterile water, and transferred to dishes containing pure cultures of the 
host. By this method reasonably pure cultures were maintained, and 
infection experiments with the host in various stages of development were 
carried on. 
B. Zoospores. 
The zoospores of the three species agree in all important features. 
They are oval to broadly elliptical, sometimes slightly reniform or anteriorly 
truncate. In motion they are usually slightly pointed at the anterior end, 
to one side of which are attached two cilia, rather close together and of 
approximately the same length. At the point of attachment of the cilia 
there is a prominent refractive spot frequently referred to as the hilum. 
With the aid of the high-power objectives, the protoplasm is seen to be 
slightly granular and not homogeneous as has been described for other 
