14 BULLETIN 1120, TJ. S. DEPARTMENT OF AGRICULTURE. 



crus t may act as a conductor of heat to the plant. In contrast with 

 this co ndition, when'the'top layer of the soil is mellow, which was the 

 conditi on in late June, as previously pointed out, the little air pockets 

 about the young plant stems tend to act as insulators and protect the 

 stems fro m the high temperatures. 



The evidence, therefore, indicates that heat canker of flax results 

 from a combination of succulence in the young plants and high tem- 

 peratures of the surface soil in immediate contact with such succulent 

 tissues. 



ARTIFICIAL PRODUCTION OP NONPARASITIC CANKER. 



A cankered condition very similar to heat canker also has been 

 produced artificially on flax. As agents, both chemicals and heat 

 were used. On July 11, 1919, 50 plants (C. I. 191) were slightly 

 burned at the soil line with concentrated sulphuric acid At various 

 intervals, from one to five minutes, the acid was washed off with 

 water. Most of the plants died when the acid was left on as long as 

 five minutes. By July 24 typical heat canker had developed on 1 7 

 of the plants that remained alive. 



On July 20, 1919, the surface soil around seven flax plants was 

 artificially heated. The flax plants were grown in pots and were 20 

 days old. A heavy aluminum wire about 14 inches in length was 

 bent to form in its center a circular loop about 1 inch in diameter. 

 The remainder of the wire led from this circle in two parallel adjoining 

 strands. The circle of wire was placed in turn over each of the seven 

 plants and buried slightly in the soil at the base of each plant in such 

 a way that the plant was in the center of the loop. The flame from a 

 Bunsen burner was applied to the ends of the wire until enough heat 

 to produce injury was conducted by the wire to the soil immediately 

 surrounding the plant. In about eight days a few of these plants 

 showed typical heat canker. 



On July 29, 1919, 12 young flax plants were sHghtly injured by 

 electrically heated wire. A loop of fine copper wire was placed 

 around each plant, barely touching the stem at the soil line, and an 

 electric current (110 volt, alternating) was passed through it. The 

 wire was immediately burned out, but the heat for the instant was 

 sufficient to cause slight injury. One flax plant of the twelve 

 showed typical heat canker on August 7. 



SIMILAR INJURY TO OTHER PLANTS. 



Similar maladies have been described or observed on various 

 plants. In one instance the senior writer noted in a field of buck- 

 wheat in central Montana a malady similar to heat canker of flax. 

 The buckwheat plants having the most typical symptoms were in a 

 portion of the field where the stand was thin. Later examination 

 showed no evidence of fungous attack. 



