December, ’20] WOGLUM AND ROUNDS: DAYLIGHT ORCHARD FUMIGATION 477 
Injury from daylight work is confined largely to the sunward side 
of the tree and its intensity at different heights is governed in great 
degree by the concentration of the gas during the exposure. This 
condition frequently reflects the method of generation, in the case 
of pot-generated gas the greatest injury being toward the top of the 
tree, the part of greatest concentration, whereas trees fumigated with 
liquid hydrocyanic acid usually exhibit injury most severe lower down 
on the sunward side. 
It is well known that at high temperatures hydrocyanic acid is more 
toxic to plants than at low temperatures. Therefore, a knowledge 
of heat conditions within the tent at the time of treatment is essential 
to a correct understanding of its bearing on plant injury. Table I 
shows the comparative temperatures at different parts of a tented 
tree in the sunshine at varying periods after covering. 
Table I.—Showing the Comparative Temperatures at Different Parts of a 12-Ft. Orange 
Tree After Covering with an 8-Ounce Army Duck Tent on A Bright Sunshiny Day in 
December. Records Taken 6 to 10 Inches from the Cloth 
Time 
Sunward side (S.) 
Shade side (N.) 
Outside tent 
Top 11 feet 
Bottom 4 feet 
Bottom 4 feet 
Direct sun 
11.00 a. m.. 
69° F. 
69° F. 
66° F. 
69° F. 
11.05 a. m.. 
76 
72 
68 
69 
11.10 a. m. 
82 
79 
68 
69 
11.15 a. m. 
87 
82 
70 
70 
11.20 a. m. 
91 
83 
71 
71 
11.30 a. m. 
92 
83 
72 
71 
11.40 a. m... 
93 
83 
73 
72 
12.00 a. m. 
95 
85 
74 
72 
An examination of this table shows that the temperature within the 
tent on the sunward side rises rapidly for the first 15 or 20 minutes 
following covering, the increase at the top of the tent after 20 minutes 
being 20 degrees higher than the outside air, an average that was 
slightly increased during the last 40 minutes of the exposure. The 
temperature at 4 feet on the sunward side was much lower than at the 
top. It is of particular interest to note that the maximum tempera¬ 
ture increase on the shaded side of the tree at 4 feet was only 5 degrees 
greater than the normal increase of the air temperature outside the 
tent and, as compared with the maximum increase near the top, 
sunward side, was 21 degrees less than this extreme. Therefore, it is 
evident that the temperature of a tree covered in the daytime is greatly 
increased on the sunward side especially at the top although the shaded 
part shows little increase above the outside air. 
Holding in mind that a strong gas is more injurious than a weak 
one, and also that toxicity increases with the temperature, it is readily 
seen that in the case of pot-generated gas where the greatest strength 
