14 BULLETIN 1120, U. S. DEPARTMENT OF AGRICULTURE. 
crust may act as a conductor of heat to the plant. In contrast with 
this condition, when the top layer of the soil is mellow, which was the 
condition 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 from 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 OF 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 17 
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 slightly 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 i 
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. 
