Jan. 10, 19x4 
Some Diseases of Pecans 
309 
From the facts that most of the infections occur within 2 or 3 feet of the 
soil surface, that such infections may take place through stomata and 
other openings in the epidermis, and that pycnidia are of rare occurrence 
upon the leaves while still attached to the tree, it seems very likely that 
the general development of pycnidia takes place upon the dead and 
decaying leaves after they have fallen to the ground and that most of the 
infection occurs through the spattering of spore-bearing material from 
the soil. 
Cultural Studies 
THERMAE TESTS 
Four series of thermal tests were carried out, corn-meal-agar cultures 
being incubated for two to three weeks at temperatures ranging from 
i° to 40° C. No change occurred at i° or at 40°, while at 5 0 and 36° 
growth, where it occurred at all, was so small as to be scarcely discernible. 
The growth of the colony was extremely slow at 8°, but increased con¬ 
siderably in rate at 12 0 . At 14 0 , 16 0 , and 20° the rate was nearly the 
same, though with a very gradual increase toward the higher tempera¬ 
ture. The optimum for the temperatures tested occurred at 30°, while 
at 32 0 growth was very similar to that at 12 0 to 14 0 . Incubation of two 
or three weeks at 37 0 to 40° invariably killed the fungus, no subsequent 
growth taking place when again held at optimum temperatures. 
Thus, incubated in com-meal-agar slant tubes, the fungus made at least 
some growth at temperatures ranging from 5 0 to 36° C. (41 0 to 97 0 F.) r 
with a very gradual decrease in rate from the optimum (30° C. or 86° F.) 
downward, and a rather rapid decrease upward. The comparatively 
high optimum temperature, together with the wide range of effective 
growth at lower temperatures, will assist in explaining the extended and 
continuous period of infection observed under held conditions. 
cueturae characters 
The more obvious characters of the fungus as grown upon a number 
of culture media are as follows: 
Beef-Agar Slant Tubes.—The colonies are at first somewhat convex, pale ocherous 
in color, with slightly roughened but glistening surface, and without aerial mycelium. 
Later, the surface becomes much wrinkled, often presents a corallike growth in the 
older parts, and approaches a light Venetian red in color. A moderate production 
of pycnidia usually takes place in cultures 1 or 2 months old. Colonies often attain 
a diameter of 10 to 12 mm. 
Com-Meal-Agar Slant Tubes (PI. XXXVII, fig. H ).—Where little aerial mycelium 
is present, the colonies are at first about the same color and general appearance as in 
the young beef-agar cultures. The cottony aerial mycelium becomes a faint pinkish 
white and is often present in considerable luxuriance. The submerged parts some¬ 
times give a pale-violet tinge to the agar, but little or no direct diffusion of color into 
the medium has taken place. Pycnidia are produced in abundance and range from 
75 to 150 ju in diameter. At first they are a pale-ocherous color, but later change to 
dark brown or almost to black. Many cross connections between the hyphae have 
