HEAT CA-NKER OF FLAX. 15 



At Fargo, N. Dak., about June 10, 1921, the junior writer and 

 Prof. H. L. BoUey observed similar injuries on wheat and barley 

 seedlings. Similar injuries were reported also about the same time 

 from other parts of North Dakota on these crops and also on oats. 

 (For soil temperatures, see Fig. 4.) 



Hartley (7 and 8) described basal lesions due to excessive heat 

 on seedhngs of conifers, rye, and cowpeas. He found that the 

 surface layer of the soil in a Nebraska nursery attained a temperature 

 of 52° C. even in the haK-shade of a lath frame. The very young 

 conifer seedlings were injured at the soil surface, where a constriction 

 formed. Later they fell over and died. The lesions usually became 

 white, and for this reason he called the trouble white-spot. 



MacMillan and Byars (10) observed a heat injury to beans in 

 Colorado. The stems were shrunken at the ground line, and many of 

 the young plants fell over. 



Miinch (12, 13, and IJi) reported soil-line heat injury on maple, 

 vetch, and peas and thought that in some cases germinating seeds, 

 as well as seedlings already emerged, are killed by overheated soil. 

 The death point for vegetative plant cells, according to Mayr {11) 

 and Miinch, lies at 54° C. Miinch records a soil-surface temperature 

 as high as 62° C. in sandy soil and states that temperatures of 50° 

 to 55° C. are reached almost daily in such soils during clear weather. 

 Schuster {20) found a stem girdling of young plants in German East 

 Africa which corresponds very closely to descriptions of heat injury 

 by Miinch and Tubeuf {21 and 22). 



Ramann {17) has seen large numbers of year-old oaks killed off by 

 heat girdling in the steppes of south Russia and has recorded there 

 soil-surface temperatures higher than 60° C. 



Hartig's {6) temperature measurements of a spruce in August show 

 how much the parts of plants are warmed above the air temperatures. 

 A temperature of 55° C. was found in the cambial region of the south- 

 west side when the air temperature was 37° C. 



Mayr {11) states that free-lying soil, especially if dark colored, as 

 is the case when it is rich in humus, can attain high temperatures. He 

 found the maximum temperature to be 68° C. In another case he 

 found a temperature of 58° C. at 49° latitude and at an elevation of 

 1,870 feet. 



Tubeuf reports soil-surface temperatures above 60° C. in the 

 United States. 



PREVENTIVE MEASURES. 



Assuming that the consistent losses from flax canker in the semi- 

 arid northern section of the Great Plains area are due to excessive 

 heat, any remedial measures would be in the nature of practices 

 which would prevent the overheating of the surface layer of the soil 

 during the seedling stage or would bring the plant past the stage of 



