May 16, 1921 
Temperature Relations of Cladosporium citri 
247 
Table I.— Range of infection as indicated 
by the four inoculation tests on citrus seedlings 1 
Plant and date of 
inoculation. 
Sour orange: 
(1) May 16,1917., 
(2) Junes, 1917.. 
(3) Sept. 24,1917. 
Pomelo: 
(4) Sept. 28,1917. 
Results of inoculation at temperature (°C.) of— 
13-5 
14 
16 
18.5 
19 
2J 
24-5 
26. 5 
27-5 
3i 
32 
32-5 
34-5 
36 
3&5 
40 
42.5 
44-5 
* Indicates definite infection; o, no infection. 
INOCULATION OF DETACHED LEAVES 
Young sour-orange leaves were detached and placed in Petri dishes, 
one set containing distilled water on which the leaves were floated and 
the other set containing cornmeal agar. Some of the fungus mycelium 
was placed in contact with the leaves, and the preparations were allowed 
to remain in the temperature chambers for 15 days. The temperatures 
used were 13.5 0 , 16 0 , 18.5°, 21 0 , 24.5 0 , 27.5 0 , and 32 0 C., with a fluc¬ 
tuation of about 0.5 0 . Infection took 'place in water at 16 0 , 18.5°, 
21 0 , 24.5 0 , and 27.5 0 , but not at 13.5° nor at 32 0 ; and in cornmeal agar 
at 18.5° and 21 0 , but hot at 13.5 0 , 16 0 , 24.5 0 , 27.5 0 , nor 32° 
INFLUENCE OF TEMPERATURE ON GROWTH AND SPORE PRODUC¬ 
TION OF CULTURES 
In addition to the inoculation experiments described above, the rate 
of growth and the formation of spores were studied with different main¬ 
tained temperatures. Distilled water, in which was floating a young 
sour-orange leaf, and cornmeal agar were used as culture media. 
Inoculation was accomplished by means of a disk (2.5 mm. in diameter) 
of agar medium bearing the mycelial weft. The cultures were kept in 
the dark, maintained temperature chambers for three or four days. 
At the end of the period the radial extension of the hyphae from the 
transferred disk, was determined. Observations were also made on the 
general abundance of spores. The data obtained are brought together 
in Table II. The growth rate is seen to have been very slow as com¬ 
pared with that of many other citus fungi (4). For the time employed 
and for the temperatures used the greatest extension of hyphae occurred 
at 2i° C. This growth rate was smaller, for each temperature, in corn¬ 
meal agar than in distilled water with the leaf, except at the two higher 
temperatures. At 32 0 no extension of hyphae was seen in water, while 
in cornmeal agar the enlargement was about one-sixth of that obtained 
at 21 0 for the same period. 
Spores were observed on the marginal hyphae in from 24 to 48 hours in 
all cases where growth was observed, except in the agar culture at 32 0 C. 
The first examination for presence of spores was made after 48 hours in the 
agar cultures. Spores were abundant at the first examination upon the 
growing hyphae of all the test cultures at 21 0 , one of the temperatures 
36732°—21 - 5 
