HEAT CANKER OF FLAX. ^ 
Table 6. — Number of flax plants not cankered and cankered in plats not shaded artd 
partially shaded by canvas, at Fargo, N. Dak., in 1920. 
Plat. 
Number of plant sill plai 
. 
Not shaded. 
Partially shaded by 
vertical ffripj t>J 
canvas. 
Not 
cankered. 
1 
Can- 
kered. 
Not i 
cankered. ; 
Car- 
kered . 
Plat G-3 
813 1 
282 ; 
1 
80 
20 
560 ' 
181 : 

Plat 1-3 

percent.. 
Total 
Cankered plants. . . . 
1 1,095 ' 
i 
1 
100 
8.4 
741 


i 
The results shown in Tables 3 and 6 are similar, in that flax plants 
grown behind canvas shades were not cankered, while some plant? 
(8.4 per cent in 1920) were cankered in the same rows where not 
shaded by canvas. 
It is to be regretted that apparatus was not at hand to take daily 
maximum soil-surface temperatures during the season of 1919. 
However, a limited number of soil-temperature readings were taken 
with ordinary thermometers. Six thermometers were placed under 
the various conditions in the plat and read at intervals. They were 
laid on the surface of the soil (or sand) and the bulbs barely covered 
with loose soil (or sand). The temperatures shown in Table 7 were 
taken on the same day at chosen places in the plat. Although the 
day was not one of the hottest of the season, it was hot enough to 
indicate the effect of shade and color of surface soil on soil-surface 
temperatures. 
Table 7. — Soil-surface temperatures, in degrees centigrade, taken in difftnnt parih of 
plat C, at Fargo, N. Dak., on July 18, 1919. 
Ther- 
mome- 
ter. 
Location. 
No. 1 On sand, in row 
No. 2 On sand, between rows 
No. 3 i On sand^ shaded by canvas. 
No. 4 On soil, in row *. 
No. 5 On soil, between rows 
No. 6 1 On soU, shaded by canvas. . 
Time of day. 
A. M. 
8.30 
9.30 
31 
30 
26 
32 
33 
27 
37 
35 
28 
36 I 
39 
29 
10.30 , 11.30 
44 
40 
28.5 I 
44 
44 
29 
P. M. 
1.00 
48 
45 
45 
45. 5 
29 
28 
49 
46.5 
49 
47 
31 
28 
2.00 
40 
41 
27 
42 
43 
28 
3.00 
34.2 
36 
27 
36 
37 
27. f 
The data given in Table 7 and presented graphically in Figure 2 
show that the rate of change of soil-surface temperatures on a hot 
day is much less rapid in the shade of a canvas 10 inches in height 
than on soil surfaces exposed directly to the sun's rays. This 
5419— 22— Bull. 1120 2 
