12 
Journal of Agricultural Research 
Voi. XXIII, No. i 
(jo). Figures A to D, in Plate 10, are photomicrographs of typical speci¬ 
mens. Two views of the same oospore are shown here, A with the focus on 
the stalk of the oogonium and B on the oospore wall. Another oospore 
and a sporangium are also in the field, but neither is in focus. C shows 
especially well the relation between oogonium and antheridium, arising 
from separate hyphae. Plate 8 includes camera-lucida outline drawings 
of oospores, with the oogonium arising from the same (H) and from 
different (G) hyphae. Oospores are thick-walled, sometimes hyaline, 
sometimes distinctly brown, depending upon the substratum. The 
irregular thickening of the outer wall of the oogonium after the oospore 
is mature, mentioned by Dastur (jo, p. 202), is often seen in oatmeal agar* 
The antheridia are variable, having been seen in all gradations from half 
the diameter of the oospore and almost square in shape to small and cir¬ 
cular in outline. Antheridia are persistent. 
Hyphae are slender, though variable, and full of granular protoplasm 
in younger cultures. A rapid flowing or streaming of the protoplasm 
has been observed under higher magnifications in young cultures on 
plates of clear com meal agar. This flowing can be seen for only a few 
seconds after the cover of the plate is removed; the drying out of the 
cultures appears to stop it. The type of mycelium varies considerably 
with different culture media. Various features described in different 
papers have been observed. There are no septa in the younger hyphae, 
but in older cultures septations are frequent. Plate 10 shows hyphae as 
seen in microscopic mounts. Irregularities of the most extreme nature, 
even approaching the tuberculate structures mentioned by Rosenbaum 
( 21 , p. 24) as a characteristic of Phytophthora syringae Klebh., have been 
seen occasionally. Hyphal walls and septations consist of true cellulose* 
Zoospore production in Phytophthora has been repeatedly described. 
The manner of their development and emergence from the sporangium 
is in this species apparently identical with that in Phytophthora para - 
sitica Dastur as described by Dastur (jo, p. 194). One feature that was 
particularly noticeable with this organism was the rapidity with which 
zoospore development occurs when a water mount is made from a culture 
of the right age and condition. When cultures are maintained at room 
temperature, zoospore production can be observed at any time within a 
few minutes. Often less than a minute from the time the mount was 
made sufficed to note the beginning of activity. Sometimes 15 or 20 
minutes are required. Normally, activity begins in less than 5 minutes, 
during which time the changes in the protoplasm can be observed. This 
feature, together with the abundance of sporangia produced on some of 
the ordinary media, the-long life of the organism in culture, and other 
characters mentioned in this paper seem, in the writer's opinion, to make 
it particularly desirable to use for laboratory study in plant pathology 
courses. 
A motion-picture film has been prepared, as noted elsewhere by God¬ 
frey and Harvey (j i), partly for the purpose of showing to best advantage 
the details of the development and escape of the zoospores. Through 
the courtesy of the motion-picture laboratory portions of that, film which 
show different stages in the process are reproduced in Plate 11. The 
first row shows the protoplasm rounded out into zoospores, with cleavage 
lines distinctly visible. This stage is more clearly brought out in Plate 
10, H, which shows a specimen killed with osmic acid fumes just previous 
to the escape of the zoospores, and treated with chloroiodid of zinc (25, 
p . 300). This stains the sporangium wall a light blue or purple and the 
