82 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
in a vigorous, thrifty condition. With two containers in each tank and 
three plants in each container, there should have been 6 plants at each 
temperature. However, the plants in one of the tanks died (table 2). 
In each experiment plants were grown for one month in inoculated soil 
at the temperatures above stated. 
Results of Experiment IV. Of the cool-soil-temperature plants, those 
grown in cool air and hot air (17 0 and 35 0 C.) showed no vascular discolor¬ 
ation; the isolation results also were negative. The plants grown in cool 
air (17 0 C.) and warm soil (27 0 C.) showed very badly discolored bundles 
at the base of the stem. This discoloration extended only a short distance 
up the stem, however, the entire stem which was surrounded* by the cool 
air appearing perfectly normal externally. When the discolored bundles 
were plated out and incubated for a few days, an abundant growth of 
Fusarium lycopersici was secured in every case. 
Plants grown in warm air (27 0 C.) and cool soil (17 0 C.) showed no 
evidence of vascular discoloration when sectioned. However, when the 
tissue from the base of the stem was plated out from each of the four plants, 
the fungus was recovered in pure culture from one of them. Warm air 
(27 0 C.) and warm soil (27 0 C.) gave 100 percent of disease, though only half 
the plants were completely dead at the conclusion of the experiment. Warm 
air (27 0 C.) and hot soil (35 0 C.) gave no evidence of vascular browning; 
the isolation results were also negative. 
Hot air (33 0 C.) and cold soil (17 0 C.) produced neither disease nor 
vascular discoloration, but the fungus was obtained in pure culture from 
the base of one plant. Hot air (33 0 C.) and warm soil (27 0 C.) produced 
the disease in virulent form, one plant escaping infection while the other 
three were diseased or dead at the conclusion of the experiment. No results 
were secured with hot air (33 0 C.) and hot soil (35 0 C.), the plants dying 
soon after they were set in the pots. 
As to the incubation period, the disease made its appearance several 
days earlier with the hot air (33 0 C.) and the #arm soil (27 0 C.) than with 
the warm air (27 0 C.) and the warm soil (27 0 C.). The rapidity of the 
development of the disease, however, was about the same with these two 
combinations. 
Results of Experiment V. The results of this experiment duplicated 
those of Experiment IV in the general temperature relations. However, 
the development of the disease was more marked than in Experiment IV 
because of the prevalence of bright, sunny weather. 
At the end of the experiment all plants were closely examined for external 
evidence of disease. They were also sectioned to determine whether or not 
vascular infection had taken place. As table 2 indicates, under the heading 
“Discoloration of Vascular Bundles,” infection of the xylem elements 
occurred in at least some of the plants at each temperature; but only 
when the infection progressed into the stem above ground were the usual 
