8 BULLETIN 1169, U. S. DEPARTMENT OF. AGRICULTURE. 
ring had come in close proximity to the bark. The trunks of the 
other trees did not show any injurious effects from the use of the 
chemical. A detailed study of the bark of some of the injured trees 
showed brown flecks in the 1920 and 1921 layers, and two flecks had 
merged into the 1922 layer. The layers inside and outside of the 
1920 and 1921 layers were practically free from flecks. The injury 
occurred over a distance of about 1 inch at the point where the crys- 
tals had been placed around the tree. There was no injury above or 
below this point. The gas passed through from 2 to 4 millimeters 
of outer bark layers without causing any visible injury. In the next 
2 millimeters of bark, which includes the 1920 and 1921 bark layers, 
brown flecks from 4 to 1 millimeter in diameter, somewhat ellipsoidal, 
the long axis parallel with the bark rays, extended to within 1 milli- 
meter of the cambium at the time of treatment. The largest flecks 
were about 3 millimeters long and 1 millimeter wide and about 10 
flecks may occur per centimeter of circumference of the tree. 
Of forty-five 4-year-old trees treated with doses varying from 14 to 
24 ounces and exposed to the gas from 4 to 12 days, 44 were healthy 
and showed no injury to the trunk. One showed some peppering. 
The 17 untreated trees were all healthy. 
On account of improper handling and neglect in the 4-year-old 
orchard, the trees had made very poor growth. Measurements of 
the trees used for paradichlorobenzene experiments in this orchard 
averaged 1 foot 1 inch in circumference, and 9 feet 2 inches in height. 
The measurements of the trees used in the 3-year-old orchard aver- 
aged 1 foot 24 inches in circumference and 10 feet 5 inches in height. 
The difference in size and vitality perhaps influenced injury on the 
4-year-old trees, where the bark layers were perhaps even thinner 
than the layers on the vigorous 3-year-old trees, which showed no 
indications whatever of injury from the use of paradichlorobenzene. 
FIVE-YEAR-OLD TREES. 
Sixty 5-year-old Redbird peach trees were treated with doses vary- 
ing from one-half to 1 ounce, 45 of which were exposed to the gas for 
periods ranging from 3 to 6 weeks, while the mounds around the remain- 
ing 15 were allowed to remain around the trees throughout the winter. 
At each examination made for tree injury no injurious effects from 
the use of the paradichlorobenzene to the trunk or tree in the case 
of these trees were observed. Forty-five trees were exposed to 14 to 
24 ounce doses for from 4 to 12 days with no injury to either the 
trunk or the tree. The check or untreated trees were in the same 
condition as the treated ones, and in no case among all the 5-year-old 
trees used for the experiment could any injury to the tree or trunk 
be attributed to paradichlorobenzene. 
SIX-YEAR-OLD TREES. 
Forty 6-year-old Redbird peach trees were treated with 1-ounce 
doses late in the fall of 1921, and the mounds left up around the trees 
over winter. Examinations made in the spring and again in July of 
1922 showed no tree or trunk injury from the late use of the chemical 
on trees of this age and from allowing the mounds to remain around 
the trees over winter. Twenty-four trees treated in the spring of 
1922 with 1-ounce doses showed no injury from paradichlorobenzene 
‘ 
