EFFECT OF THALLIUM ON PLANT GROWTH 7 
during the first day, and practically all within a week. Therefore, 
the aidbuted thallium is removed from the surface before it can 
produce any effect on the vegetation. 
Repeated studies of range areas treated as often as nine times 
failed to show any damage to vegetation. With removal of the 
ground squirrels the soil returns to a proper condition, and normal 
plant growth rapidly occurs. In general, the use of thallium in 
rodent control has consistently increased the (grow th of vegetation 
from 10 to 25 percent, without any evidence of damage to soil fertility. 
A few experiments were conducted to determine whether thallium 
compounds would prove suitable as weed killers. Azbes were placed 
in pots of soil and treated with varying concentrations of thallium, 
up to the rate of 1,280 pounds per acre. No injurious effects were 
observed over a period of 8 weeks. This suggests that such hardy 
plants as Ribes are more resistant than grains and grasses. 
Assuming, for comparative purposes only, that the action of applied 
thallium would be localized in the upper 3 inches of soil: Then, 1 
acre, or 43,560 square feet, one-fourth foot deep would correspond. to 
approximately 10,000 cubie feet of soil and would weigh approxi- 
mately 1,000,000 pounds. Under this assumption, 10 pounds of 
thallous sulphate per acre would correspond to 10 parts per million, 
and the results on a field scale are in harmony with those in the 
laboratory. 
J CONCLUSIONS 
Under laboratory and field conditions on various types of soil, the 
addition of thallium compounds up to 10 parts per million (10 pounds 
of thallous sulphate per acre, equivalent to 1,000 pounds of thalgrain 
per acre) had no injurious effects on vegetation, and in many instances 
appeared to stimulate plant growth. 
With the application of larger quantities, injury was observed. 
Under field conditions no damage occurred during 9 months of dry 
weather, but it developed following the rainy season. 
Thallium compounds when applied to the soil in varying concen- 
tration up to 1,280 pounds per acre failed to kill or apparently even 
to injure fibes in 8 weeks. 
In control work, ground squirrels consumed thalgrain so rapidly 
that no damage to plant growth was found on areas treated as fre- 
quently as nine times. 
Under the conditions used in the control of rodents by properly 
trained personnel, no evidence of injury to vegetative growth by 
thalgrain has been found. 
LITERATURE CITED 
(1) Barnum, C. C. ; 
1930. RAT CONTROL IN HAWAII. Hawaii. Planters Rec. 34: 421-4438. 
(2) BaTEMAN, 
1933. THE EFFECT OF CONCENTR ADS ON THE TOXICITY OF CHEMICALS TO 
LIVING ORGANISMS. U.S&. Dept. Agr. Tech. Bull. 346, 54 pp. 
illus. 
(3) Borreer, R. 
1863. UBER DAS VORKOMMEN DES THALLIUMS IN SALINISCHEN MINERAL- 
WASSERN, INBESONDERE IN WASSER DES NAUHEIMER SPRUDELS. 
Liebig’s Ann. Chem. 128: 240-247. 
(4) Brooks, S. C. 
1932. THALLIUM POISONING AND SOIL FERTILITY. Science (n. s.) 75: 
105-106. 
