217 
Species of Olpidiopsis , (Cornu) Fischer . 
has carried on no controllable experiments in reference to this point, but is 
convinced from careful observations that there is some varying attractive 
force exerted by the host hyphae on the zoospores of the parasite. 
De Bary was inclined to the view that by the secretion of some 
chemical substance the oogonia of Saprolegnia may be capable of inducing 
the formation of antheridial branches. This assumption is strengthened by 
the work of Kauffman (16), in which he showed how the development 
of sexual organs of Saprolegnia , especially antheridia, could, to a certain 
extent, be controlled by the use of chemicals. 
A. Fischer (12) theorizes that different organs of Saprolegnia, such as 
young hyphae, gemmae, and oogonia, perhaps give off different metabolic 
substances, and further that such substances vary in different genera. 
These diffuse into the surrounding water and within a certain radius exert an 
attractive or repellent force on the zoospores of the parasite. 
D. Development of the Sporangia. 
Growth period. After the penetration of the zoospore into the host, 
it can frequently be observed for a brief time as a small, more or less 
refringent mass of the protoplasm (Figs. 4, 10). It exhibits slight changes 
in shape, and in the course of an hour or so is entirely lost to view. The 
young parasite is now more or less surrounded by the host protoplasm, at 
the expense of which it begins to grow rapidly, and at the same time it 
exerts upon the host a stimulus which causes, frequently in a few hours, an 
abnormal development of the infected hypha (Figs. 7, 11, 76). Usually the 
parasite undergoes its development at or near the point of entrance. Frequent 
exceptions to this condition have been observed, however, and are also noted 
by Fischer for Olpidiopsis ( P seudolpidium ). 
The change of position is very probably passive and due to currents of 
host protoplasm. In cases where a number of sporangia occur in the 
same intercalary swelling there seems to be no other explanation than that 
some of the young parasites migrated to that point. Growth of the infected 
hyphae beyond the position of the parasite usually ceases soon after its 
infection, especially when such takes place near the end. 
In the early stages of development the parasite contains few granules 
scattered through the homogeneous ground substance, most of them lying 
about the periphery (Fig. 12). There soon appear a number of larger 
granules which grow rapidly and present the appearance of being of a fatty or 
oily nature (Figs. 12, 13, 17). They frequently exhibit a vacuolate character, 
and show marked changes in form (Figs. 13, 23). Similar granules have 
been observed by Zopf in O. Schenkiana and by Fischer for both species of 
Olpidiopsis (P seudolpidium) studied by him. 
The parasite now becomes surrounded by a hyaline wall. The proto- 
