HEAT CANKER OF FLAX. 



Table 6.- 



-Numher of flax plants not cankered and cankered in flats not shaded and 

 partially shaded by canvas, at Fargo, N. Dak., in 1920. 





Number of plants in plat. 



Plat. 



Not shaded. 



Partially shaded by 

 vertical strips of 

 canvas. 





Not 

 cankered. 



Can- 

 kered. 



Not 

 cankered. 



Can- 

 kered. 



Plat G-3 : 



813 



282 



80 

 20 



560 

 181 







Plat 1-3 











Total 



1,095 



100 



8.4 



741 







Cankered plants percent. 















The results shown in Tables 3 and 6 are similar, in that flax plants 

 grown behind canvas shades were not cankered, while some plants 

 (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 different parts of 

 plat C, at Fargo, N. Dak., on July 18, 1919. 







Time of day. 



Ther- 

 mome- 

 ter. 



Location. 



A.M. 



P.M. 





8.30 



9.30 



10.30 



11.30 



1.00 



2.00 



3.00 



No. 1 



On sand, in row 



31 37 

 30 35 



26 28 



32 36 



33 39 



27 29 



44 



40 



28.5 



44 



44 



29 



48 

 45 

 29 

 49 

 49 

 31 



45 



45.5 



28 



46.5 



47 



28 



40 

 41 

 27 

 42 

 43 

 28 



34.2 



No. 2 



On sand, between rows 



36 



No. 3 



No. 4 



On sand; shaded by canvas 



On soil, m row 



27 

 36 



No. 5 



On soil, between rows 



37 



No. 6 



On soil, shaded by canvas . . 



27.5 















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 



