264 FUMIGATION METHODS 
produce a death atmosphere than will be needed ina 
soil of much greater depth. In soils of the same 
character and condition the amount needed will be 
proportional to the permeable depth of the soil. In 
heavy, compact soils increase the number of injections 
and diminish the dose; in light, deep, permeable soils 
decrease the number of holes and increase the dose. 
In field experiments with the grape, using plain 
carbon bisulphid in quite fresh soil, vines withstood 
105 c. c. of carbon bisulphid, nearly 4.4 ounces, 
divided equally among three holes placed about 16: 
inches from the base of the vine and at a depth of about 
20 inches; but 180 c. ¢c., 7% ounces, proved fatal to 
the vines. In warmer, drier, more shallow soil a dose 
of 90 c. c. per vine, similarly placed, proved fatal. 
After considerable rain, when the ground was quite 
wet, a vine withstood 260 c. c. of carbon bisulphid, 
and some vines are said to have withstood 4oo c. ec. 
The treatment should never be applied for some time 
after plowing or cultivating, as a firm, compact, moist 
surface is much more favorable to the retention of the 
vapor. For the same reason about fifteen days should 
be allowed after treatment before cultivation is re- 
sumed. If the soil is either very wet or dry, treatment 
should be withheld. To be in the most favorable con- 
dition for treatment, the soil should be quite moist and 
moderately permeable, with a firm, even surface, well 
compacted by rain and having a depth of at least eight 
inches. 
The extent of diffusion of the vapor determines the 
distance apart at which the injections must be made to 
reach all parts of the soil evenly and effectively. This 
