Feb., 1923] 
CLAYTON — TEMPERATURE AND FUSARIUM WILT 
8l 
These experiments showed, then, that there are ranges of soil tempera¬ 
ture, approximately 14 0 to 20° C. and 34 0 to 35 0 C., which permit growth 
of both the plant and the fungus separately, but which do not favor the 
parasitic development of the fungus within the host. 
2. Experiments in which both air and soil temperatures were varied 
Early in these studies it became apparent that, although this fungus 
entered the plant through the root, it made its way into the aerial stem and 
did its damage in the above-ground parts. The roots appear to die last, 
the sequence being: leaves, then the main stem, and finally the roots. 
From previous work with soil temperature, the conclusion was drawn that 
soil temperature is a controlling factor only so long as the fungus is in the 
soil or roots, and probably exerts little or no influence after the fungus has 
grown up out of the soil. Thus it seemed logical to suppose that, once the 
plant parts above ground are diseased, air temperature alone might in¬ 
fluence the progress of the wilt. In order to determine whether or not 
this is the case, experiments were conducted in which air temperatures as 
well as soil temperatures were varied. 
Methods. Three sections of greenhouse were used in these experiments, 
with air temperature controlled at approximately 17 0 , 28°, and 33 0 C., 
respectively, by methods to be described in detail in a later publication. 
Unfortunately the ranges of air temperature procured were subject to 
considerable fluctuations, since in chambers where the bright sunlight is not 
counteracted in some way no ordinary means will prevent a rise in tempera¬ 
ture. In reality, three ranges of temperature were obtained: a cool range 
of from 15 0 to 25 0 C., a warm range of from 25 0 to 30° C., and a hot range 
of from 30° to 35 0 C. In each of these sections a set of three constant- 
temperature tanks was placed. These tanks were maintained at 17 0 , 27 0 , 
and 35 0 C., to correspond with the air temperatures. Thus, by controlling 
both air and soil temperatures, nine combinations of soil and air tempera¬ 
tures were obtained (table 2). 
Two experiments were conducted under these conditions of temperature. 
In Experiment IV the soil was steam-sterilized as usual and placed in the 
temperature-tank containers, and a spore suspension of the fungus was 
poured on the surface. Mineral wool, packed closely around the stems of 
the plants after they were set, served as insulating material. Two well- 
developed plants were used in each can. 
In Experiment V, very small seedlings were transplanted into the 
sterilized soil of the containers and allowed to grow at 15 0 to 18 0 C. for a 
month, after which period the containers were transferred to the tempera¬ 
tures to be used throughout the experiment and incubated there for several 
days before the inoculum, a spore suspension, was added. A layer of mineral 
wool over the surface of the soil was used for insulation. At the beginning 
of the experiment the seedlings had attained a height of 3 inches and were 
