72 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
Ohio, and Tennessee. In order to make sure that this Indiana strain 
chosen was representative among these isolations when inoculated plants 
were grown at different temperatures, a number of tomato plants were 
inoculated with it, an equal number with the Tennessee.strain, and several 
pots of each were grown at several temperatures. The results in the two 
series were remarkably uniform. The amount of disease produced at each 
temperature was nearly equal in plants inoculated with the Indiana strain 
and in those inoculated with the Tennessee strain. Also, when pure 
cultures of the two strains were incubated together at different temperatures 
(for methods, see page 78), their respective optimum, maximum, and mini¬ 
mum temperatures for growth were found to be the same. 
Identification. In order to insure confidence as to the identity of the 
organisms in hand, morphological and cultural studies were made following 
the methods of Sherbakoff (12). The Indiana strain was made the basis 
of these, with some comparative studies upon the other strains. The spore 
counts and measurements were made from 15-day-old cultures grown at 
28° C. The following media were used: clover stems, tomato stems, potato 
plugs, rice, beans, potato agar (both 2 and 5 percent glucose), oat agar, 
malt agar, and water agar. It was found, however, that all the vegetative 
and reproductive parts of the fungus and all the color changes produced in 
any of these media were found on rice, tomato stems, and oat agar. The 
identification work consisted of observations as to the color and type of 
growth, the production and appearance of sclerotia and sporodochia, the 
character, septation, and size of macroconidia, and the method of bearing 
the chlamydospores. 
These studies justified the conclusion that the organism in hand was Fu- 
sarium lycopersici Sacc., and that, although there are minor variations in 
pathogenicity and other characters, the Fusarium wilt disease of the eastern 
United States is probably all attributable to this one species. 
Temperature Relations of the Fungus in Pure Culture 
In order to determine the range of temperatures through which F 
lycopersici grows vigorously, pure cultures of the Indiana strain were 
prepared as follows: A small drop of a spore suspension made from a single¬ 
spore culture was placed in the center of each of a series of Petri dishes 
containing potato hard agar. These Petri-dish cultures were incubated at 
28° C. for 24 hours and examined under the low power of the microscope. 
All cultures in which no spores had germinated, or which contained more 
than two or three germinating spores, were discarded, and three of the 
remaining dishes were incubated at each of 12 graduated temperatures, 
ranging from 4 0 to 38° C. It was found by daily observation that after 
six to eight days the fungous growth at temperatures approaching 28° C. 
entirely covered the surface of the dish. Plate VIII shows representative 
Petri-dish cultures after incubation for five days at each of the temperatures 
