Mar., 1923] CLAYTON-SOIL MOISTURE AND FUSARIUM WILT 
147 
It will be observed that the disease affected the plants growing in soils with moistures from 
20 to 32 percent. One of the plants in the 20-percent crock was still alive at the time the 
photograph was taken, while both plants in the 23.5- and 32-percent crocks had been dead 
and dry for some days. 
Plate XIV 
A. These plants had been growing with moistures of 14, 18, 25, 30, and 35 percent 
(saturation) for two weeks. The soil was inoculated with Fusarium lycopersici in pure 
culture. Infection showed in the 25- and 30-percent crocks the day after the photograph 
was taken, and within two weeks these plants, which were making the most rapid growth, 
were dead. The temperature ranged from 25 0 to 30° C. 
B. Four of the five crocks of plants shown in figure A, the 18-percent soil-moisture 
crock being omitted because of lack of space. This photograph, taken two weeks after 
the one above, shows how the wilt disease attacks and destroys tomato plants growing 
under good conditions, while plants growing in very dry soil (14 percent) or saturated 
(35 percent) were not attacked. The semi-wilted condition of the plants growing in the 
crock of soil held at 14 percent soil moisture is due to moisture shortage, not to attack by 
the disease. 
Plate XV 
The plants in lots A, B, C, and D were grown five weeks in sterilized and inoculated 
soil, with temperature conditions favorable for the development of the disease. 
The following sets of soil-moisture conditions were maintained: 
Lot A : 5 weeks with moist soil. 
Lot B: 1 week with dry soil, 4 weeks with moist soil. 
Lot C : 4 weeks with dry soil, 1 week with moist soil. 
Lot D : 5 weeks with dry soil. 
The photographs were taken at the end of the five-week period. The disease developed 
with maximum virulence in lot A; in lot B, the plants were almost as severely affected; 
lot C had only one plant affected by the wilt; lot D showed no disease. The development 
of the disease was thus directly in proportion to the amount of moisture supplied. It is 
interesting to note that in lot B, one week of dry soil conditions having preceded four weeks 
of moist soil conditions, the incubation period for the disease was 22 days, while in lot A, 
good moisture conditions having been maintained for five weeks, the incubation period 
was 15 days. 
