248 
Journal of Agricultural Research 
Vol. XXI, No. 4 
at which infection of rapidly growing sour-orange seedlings and detached 
sour-orange leaves had been observed to be pronounced. Spores were 
also abundant in the water preparations at 24.5 0 and 27.5 0 after 24 hours, 
and in the preparations of agar at 24.5 0 after 48 hours; at these tempera¬ 
tures no infection had occurred in the tests with growing plants, but a 
slight infection had been observed after 1 o days on detached leaves in water. 
Spores that had fallen from the hyphae in certain ones of these cultures 
were found to have fallen on the surface of the medium at some distance 
laterally from the ends of the aerial hyphae on which they had been 
borne. Apparently these spores had been ejected with considerable 
force from the ends of the hyphae. In one case at 16 0 C. a fringe of spores 
was observed, most of them at least 210 microns distant from the ends of 
the outermost hyphae. This feature of spore dispersal in cultures had 
previously been seen but not recorded. It was noted as most frequent 
after four days in cultures growing at the* edges of leaves in cornmeal 
agar at 16 0 , 18 0 , 21.5 0 , and 24.5 0 . 
In the 16° preparation with water and a sour-orange leaf, spores were 
observed to be mostly formed on the tip ends of the outwardly extending 
aerial hyphae at some distance from the floating leaf. They were nearly 
hyaline at first, subsequently becoming slightly dusky. Most of them 
were i-celled, but a few were 2-celled. Detached spores were germi¬ 
nating from the ends of spores in line with the longest axis. Hyphae were 
hyaline when viewed singly, but were pinkish or flesh-colored in mass. 
On cornmeal agar under the same conditions spores were forming with 
from two to four in a chain, and the ejected spores were germinating 
on the surface of the medium. 
The influence of temperature on the vegetative hyphae was marked. 
At 27.5 0 and 32 0 C. in the cornmeal agar preparations the hyphae were 
broad and straight, 8 to 12 microns or more in diameter. At 23 0 and 21 0 , 
on the other hand, the hyphal diameter was only one-half as great and 
the hyphae were more bent and tortuous. At 18.5 0 , 16 0 , and 13 • 5 0 > 
the hyphae were broader, much as at the higher temperatures. 
Table II .—Growth and spore formation in Petri-dish cultures of Cladosporium citri at 
different maintained temperatures 
Temperature. 
Fungus floating in water with tender leaf. 
In cornmeal agar. 
Radial 
growth in 
3 days. 
Spore formation. 
Radial 
growth in 
4 days. 
Spore formation. 
In z day. 
In 3 days. 
In 2 days. 
In 4 days. 
°C. 
I 3 - 5 
16 
18.5 
21 
24- 5 
27-5 
32 
Microns. 
62 
170 
285 
655 
38S 
*54 
0 
Few. 
...do. 
...do. 
Abundant.. 
... do. 
...do. 
None. 
Few....... 
Abundant.. 
Few. 
Abundant 1 . 
Abundant.. 
Abundant 1 . 
None. 
Microns. 
38 
92 
Il6 
370 
323 
197 
62 
Few. 
...do. 
...do. 
Abundant 1 . 
...do. 
Few. 
None. 
Few. 
Do. 
Do. 
Abundant. 
Do. 
Few. 
None. 
1 Spores found some distance laterally from ends of the outermost hyphae as if ejected with considera¬ 
ble force. 
