G 2 
Mycologia 
thicker and more transparent cell wall than is found on the re- 
mainder of the conidinm. The conidia are ovate, or obpyriform 
due to subapical constriction, and average 20 X 30 ^ . They are 
also very much crowded on the conidiophores which are not so 
highly developed as in P. infestans, nor are the conidia produced 
in such great numbers as in that species. Theii* germination was 
not noted. 
The gametes are produced on separate hyphae, and at first are 
not well differentiated from other hyphal outgrowths. The 
antheridium, which is the first to appear, is a rounded or oval 
structure, borne laterally on the hypha from which it is soon 
separated by a septum. Sometimes, however, the antheridium 
is a true intercalary cell. In time the antheridium becomes filled 
with a very dense mass of granular protoplasm, apparently at the 
expense of the parent hypha as this becomes empty. The 
oogonial progamete arises in a similar manner, first appearing as 
a swollen knob-like body. If it comes in contact with the 
antheridium it grows in such a manner, as to penetrate it. The 
duration of this condition and the accompanying cytological phe- 
nomena have not been determined, but after a few hours, and 
apparently only at night, the oogonium bursts out of the antherid- 
ium and completes its development. The oogonial wall is usually 
thinner than that of the antheridium. As the oogonium attains 
its full size protoplasm ceases to migrate into it and its stalk 
becomes plugged, although no septum is formed. By this time the 
parent hypha is almost emptied of protoplasm. During the later 
stages of the development of the oogonium and just prior to the 
contraction of the protoplasm and its separation from the wall of 
the oogonium the contents of the antheridium begin to disappear, 
but in what manner was undetermined. At maturity the oosphere 
occupies the upper part of the oogonium, which is composed of 
the entire protoplasmic contents of the oosphere except small 
particles which adhere to the oogonial wall. The oosphere now 
begins to form a wall about itself, which utlimately is about 2 p 
thick, smooth, and yellowish-brown in color. The mature 
oogonium is about 3 6 /j. in diameter with a colorless wall which 
is less brittle than that of P. infestans. The oospores are about 
29-3 °A l in diameter, or considerably smaller than those of P. 
