Nov. 3, 1923 
Helminthosporium Disease of Wheat 
197 
belief that climatic factors and weather conditions probably exerted 
some influence on the development of the disease. Accordingly, labora¬ 
tory and field experiments were planned whereby data on these influences 
might be obtained. Since H. sativum attacks all parts of the plant it is 
obvious that the different types of injury should be studied more or less 
independently. In view of this fact it was decided to make the pre¬ 
liminary studies on those injuries which are confined to the subterranean 
parts of the plant, and on the development of these injuries as influenced 
by soil temperature and soil moisture. 
GREENHOUSE EXPERIMENTS 
SOU, TEMPERATURE STUDIES 
All of these studies were carried out in the department of plant 
pathology, University of Wisconsin. The soil-temperature apparatus 
used was essentially the same, except for some modification, as that 
described by Jones (7). 
The wheat seedlings were grown in metal pots 8 inches in diameter 
and 9% inches deep, placed in tanks of water held at the desired tem¬ 
peratures. The water line came from % to 1 inch above the soil line in 
the pots. Previous experiments with potatoes in connection with the 
soil-temperature studies on potato scab by Jones, McKinney, and Fellows 
(8), and also preliminary experiments with wheat plants, showed that 
there was no need for drainage in the metal pots, and, therefore, no 
special drainage apparatus was used. 
EXPERIMENTS AT CONSTANT TEMPERATURES 
Experimental Methods 
The various temperatures were maintained by electric heaters placed 
on the bottoms of the tanks in contact with the water, and by means 
of cold running water supplied from the local mains in winter and 
from a refrigeration coil in summer. The high temperatures were con¬ 
trolled by electric thermostats which opened and closed the heater 
circuits by means of relays. These regulated to within an average of 
X° to C., above and below the stated temperature. The low tem¬ 
peratures were regulated by carefully adjusting the inflow of cold water 
or by a controlled electric heater which operated against a stream of cold 
water having an inflow slightly greater than that required to hold the 
proper temperature in the soil. All temperatures were regulated and 
recorded on a basis of the temperature of the soil 1 inch below the surface 
and 1X inches from the walls of the pots. 
All plants were watered on a basis of weight with tap water frequently 
enough to insure a nearly constant soil moisture throughout an experi¬ 
ment. At the high temperatures pots were watered daily or oftener, 
depending upon the weather, while at lower temperatures the watering 
was less frequent. Different methods have been used, but in this work 
it seemed that the application of water directly to the surface of the soil 
was best when watering was done frequently. In all the experiments, the 
plants in a given soil-temperature series were subjected to the same air 
temperatures, which ranged from approximately 18 0 to 24° C., accord¬ 
ing to the season. The differences in host response and the development 
of disease were due, therefore, primarily to differences in soil temperature. 
All soil used in the soil-temperature studies consisted of a fertile loam 
obtained from a wood lot. Although this soil had never been cropped it 
