294 RepPortT oF THE DEPARTMENT OF ENTOMOLOGY OF THD 
EFFECT OF THE GAS ON TREES. 
In the preliminary work on fumigation, in California, espe- 
cially of citrus trees, all injury to the leaves of the trees was 
supposed to result from decomposition of the gas by sunlight 
and heat. As a result fumigation is usually done at night in 
that section, although it was found that by the use of black tents 
the work could be done in the day time with less injury than 
with uncolored tents. In the east the majority of the tests have 
been made with black tents at a season of the year when the 
trees were dormant, with the result that there was little or no 
danger of injury from the conditions that orange growers have 
to contend with. The principal injuries to deciduous trees 
result from other causes, such as too heavy charges of chemi- 
cals, over exposure or treatment after leaves have begun to 
expand. 
In the following tables are shown some of the effects of differ- 
ent amounts of chemicals allowed to act for varying lengths of 
time, together with notes on the same. In a study of these 
tables the following notes will be of assistance: 
The chemical abbreviation KCN is used for potassium cyanide, 
the chemically pure (approximately 98 per ct.) being used in all 
cases. In most instances the maximum exposures were made 
during the noon hour and comparatively few trees were treated 
for long periods; in addition the number of trees receiving heavy 
charges of KCN were small; hence the tables cannot be 
averaged. 
The orchards in which the tests were made consisted of a 
mixture in one case of apple, cherry, peach, pear and plum; in 
the other of apple, cherry, chestnut, peach and walnut. In the 
first, a small orchard, the trees were set haphazard; while in the 
second, a peach orchard, the peach trees in every other row 
alternated with apple, cherry, chestnut or walnut. No definite 
order was followed in setting the alternating trees; and as a 
result there were but few apples, walnuts, etc., and these were 
often widely scattered. 
