402 
Journal o f Agricultural Research 
Vol. XXIX, No. 8 
brown discoloration and soft rot which 
spread upward with decreasing rapidity, 
finally stopping within six to eight 
days at some point 20 to 40 mm. up 
the stem. Below this point the decay 
continued until the epidermal cylinder 
and the fibrovascular system alone 
were left. Oospores could be found in 
infected tissues within four days after 
inoculation. Reisolation of the organ¬ 
ism and successful inoculations with 
the reisolation completed the patho¬ 
genicity cycle. In checks where the 
severed surface was not inoculated a 
callus and roots soon formed, binding 
the plant into the soil, in sharp con¬ 
trast with the loose condition of 
inoculated plants. 
In one experiment in which cuttings 
were placed in pots which had pre¬ 
viously contained artificially infected 
plants, two out of five developed the 
stemrot, and the typical oospores 
were found in the tissues, indicating 
the r61e of infected soil as the carrier 
of inoculum. The large number of 
oospores usually formed and set free 
by decay of the host cells is doubtless 
a fruitful source of infection. Since 
their germination has not been ob¬ 
served, however, even after three 
months, it seems more likely that the 
primary source of infection lies in the 
mycelium and sporangia in decayed 
tissues, although the latter are not 
formed so abundantly as the oospores. 
Cross-inoculations on cucumber, 
water cress, and radish seedlings in 
pots and in sterile tube cultures were un¬ 
successful, except that superficial black 
streaks appeared on the radish stems 
without progressing much farther or 
causing any wilting. Infection was 
obtained on Coleus cuttings, which 
were rapidly discolored and subjected 
to a shriveling dry rot without any 
stoppage of infection as in the case of 
geranium cuttings. 
Measurements of the progress of 
infection in the latter were made in two 
experiments, including 9 and 10 in¬ 
fected plants, respectively, and are 
plotted in Figure 1. 
SUMMARY OF INOCULATION EXPERI¬ 
MENTS 
Dec. 3 , 1919.—Twelve cuttings inoc¬ 
ulated at the surface of the 
ground, six of these without 
wounding; five checks. All 
the plants were covered 
with bell jars. No infec¬ 
tion after three weeks in 
checks and uninjured cut¬ 
tings, callus and roots form¬ 
ing normally; discoloration 
and decay followed wound 
inoculations, rotting entire 
base but stopping above 
ground within six to eight 
days. Reisolations made 
December 8 yielded 11 sim¬ 
ilar colonies of slow-grow¬ 
ing type with combed-silk 
effect, like original. Typ¬ 
ical oospores appeared on 
all the colonies. 
Jan. 6 , 1920;—Six cut¬ 
tings inoculated at surface 
of ground, with slight scal¬ 
pel injury; 10 inoculated at 
freshly cut base; six checks. 
Spreading discoloration 
visible the next day, except 
iix two inoculated at surface, 
in which the inoculated 
area dried up and remained uninfected. 
By the eighth day decay had progressed 
up the stem from basal infections and 
had stopped with sharp demarcation. 
Lateral infections spread in both direc¬ 
tions, destroying tissues below. The 
checks were healthy and formed roots. 
Feb. 16, 1920.—Four cuttings in¬ 
oculated with one of the December 8 
reisolations. All blackened on fifth 
day 8 to 22 mill, up to the stem; no 
further progress after ninth . day; 
oospores abundant in the tissues. 
One check. This remained healthy. 
M ar. 3 , 1920.—Ten cuttings in¬ 
oculated at base with original isolation. 
Eight infected; blackening progressed 
11 to 20 mm. by fifth day. Further 
advance very slow, stopping at eighth 
day. Two inoculated plants and four 
checks remained healthy. 
Fig. 1.—Graph showing progress of discoloration of inoculated 
geranium cuttings, 2 experiments, averages of 9 and 10 plants, 
respectively 
