H 
Journal of Agricultural Research voi. xxiii, no. i 
2 per cent osmic acid. This killed the spores instantly. Then very dilute 
aqueous gentian violet solution was applied, resulting in the immediate 
staining of the spores. The flagellae too, being at rest, were distinctly 
visible, and in certain cases their position would seem to indicate their 
instantaneous cessation of normal active motion. The osmic acid dark¬ 
ened the oil contents of the spores sufficiently to interfere with the view 
of the structure of the protoplasm; consequently no attempt was made 
with this material to draw the cell contents. Figure A of Plate 9 shows 
spores in varying positions, with flagellae. Figure B shows different 
stages in their deliquescence and disappearance. Here is seen a rounded 
spore that has come to rest with the droplets still attached. Figure C 
shows zoospores that are abnormal or that had not sufficient time, 
before being killed, to round out into normal. 
Within an hour or two after motility ceases zoospores often begin 
to germinate. Plate 9, D, consists of drawings of germinating zoospores 
in different stages of growth. Germination in water sometimes results 
in the formation of small conidia, normal in appearance, as shown in F. 
These may produce zoopores, or may germinate by germ tubes and 
continue the vegetative growth. At times also small chlamydospores 
may be formed (PI. 9, E). Germination on a plate of com meal agar 
resulted in the development of normal vegetative hyphae such as occur 
when the host plant is infected with zoospores. Figures K, L, and M 
in Plate 10 consist of photomicrographs of germinating zoospores in 
different stages. 
cultural characteristics 
The appearance of this Phytophthora, as of others, differs considerably 
on different media. It was not grown on an extensive list of media 
for the express purpose of making comparisons, but on those used for 
special purposes, observations were made as follows: 
Corn meal agar (30 gm. corn meal, 20 gm. agar, 1,000 cc. water). 
At first growing on and beneath the surface, the organism very quickly 
(usually by the second day) produces aerial hyphae which, in mass, 
present a loose, fluffy, semitransparent appearance rather than a pure 
white, cottony appearance, such as occurs with many fungi producing 
colorless hyphae. Mature sporangia may be found on the fourth day, 
though they are not present in greatest abundance until the culture is 
from 10 days to 2 weeks old. Chlamydospores and oospores may often 
be found attached to the glass above the surface of the medium, especi¬ 
ally if a thin layer of the agar were left there while the tube was being 
slanted. 
Oatmeal agar (100 gm. ground Quaker oats, 20 gm. agar, 1,000 cc. 
water). The growth is similar to that on com meal agar, except that 
the aerial mycelia become more dense. This medium is very good for 
the development of oospores, which occur profusely in the surface layer 
after it dries out a little. 
Lima bean agar (100 gm. lima beans in 2 per cent agar). Growth is 
similar to that on corn meal agar, except that the surface and subsurface 
development is more pronounced and of longer duration before the 
aerial hyphae develop, and the latter growth is not nearly so dense. 
This medium is a very good indicator as to the purity of a culture. 
Bacterial contaminations become evident very soon, if they are present. 
It is also good for the production of oospores, which are sometimes found 
in great abundance embedded in the surface layers. 
