2 1 6 Barrett . — Development and Sexuality of some 
tion. No complete observations relative to this point have been recorded, 
so far as I am aware, for any Olpidiopsis species parasitic on the Sapro- 
legniaceae. 
Cornu (6) briefly describes this phenomenon for certain species studied 
by him, while A. Fischer (12), for Olpidiopsis (Pseudolpidium) i Woronina , and 
Rozello , records his very careful observations as to both penetration and 
subsequent development of the parasite. 
The zoospores, after a swimming period, the length of which seems to 
depend considerably on the age and condition of the culture in which it 
occurs, finally settle down on some favourable part of the host and either 
produce infection or die. There is at first a slight amoeboid movement, 
followed by a rounding up of the zoospore body and the formation of 
a wall (Fig. 3). After resting in this condition for fifteen minutes to one 
hour, the encysted spore produces from the side in contact with the host 
a short cylindrical tube which penetrates the wall of the hypha. During 
this process the zoospores become pushed slightly away from the filament. 
The penetration tube varies somewhat in length in the different species, 
being shortest in O. luxurious , and longest in O. vexons (Figs. 4, 8, and 9). 
After the formation of the tube, the appearance of a small vacuole in the 
spore body indicates that the passage of its contents into the host has 
begun. As observed by A. Fischer (12) and Butler (4) this tube is so small 
that it is impossible to observe the passage of the protoplasm through 
it. Occasionally it could be seen extending into the cell cavity beyond the 
limits of the wall (Fig. 9). 
By far the majority of zoospores in all three species fail to infect the 
host. A greater percentage succeed in O. luxurious than in the species 
on Soprolegnio , due, no doubt, to the fact that infection in this species is 
not so nearly confined to the young hyphae. Those zoospores which fail 
to enter the host die sooner or later, either by a direct disintegration of the 
protoplasm, or after germination. In the presence of the host, and usually 
near or in contact with the hyphae, zoospores frequently put out long 
slender germ tubes. These have been observed in large numbers on old 
empty sporangia of Aphonomyces and on the old threads of Soprolegnio . 
The germ tubes sometimes entirely surround the hyphae ; in other cases 
they may extend some distance parallel to them (Figs. 5, 6). As has been 
observed by A. Fischer, the life of the zoospore is much longer in the 
presence of the host than in pure water. 
The germinated zoospores of Aphonomyces are frequently infected by 
O. luxurious (Fig. 10). As many as four developing sporangia of the 
parasite have been found in a very short germ tube. In no case was 
an infection of gemmae or reproductive organs of Soprolegnio observed. 
Just how far, if at all, chemotropic stimuli set up by the host influence 
the behaviour of the parasite zoospores is impossible to state. The writer 
