BULLETIN 1120, U. S. DEPARTMENT OF AGRICULTURE. 
Numerous inoculations with fungi and bacteria from these isolations 
always failed to produce symptoms identical with those of the type 
of flax canker under consideration. Hence, this preliminary work 
indicated more and more clearly that this tjrpe of flax-canker injury 
was due to causes of a nonparasitic nature. 
FIELD OBSERVATIONS. 
A number of observations had tended to indicate that excessive 
heat at the soil line during the seedling stage possibly was the cause 
of the trouble. For a number of years it had been noticed at Mandan, 
N. Dak., that flax cankered more in the nursery plats than in the rota- 
tion plats. In the former the rows were spaced rather widely, flax 
was sown rather thinly, and the plats were kept free from weeds. In 
the rotation plats the rows were closer together, the flax was sown 
more thickly, and weeds were allowed to grow. As a result of these 
two sets of conditions, the soil was much more exposed to the intense 
sunlight in the nursery plats than in the rotation plats. Indications 
pointed, therefore, to intense sunlight as being the most important 
factor in causing canker. Furthermore, for a considerable time it had 
been noted that flax canl^er had been most severe in flax on breaking 
(freshly turned sod) , where weeds are practically absent and a thin 
stand usually occurs. By contrast, flax fields on old land usually are 
weedy. This canker, therefore, developed both in the nursery and in 
fields under similar conditions; that is, the most canker occurred 
where conditions made it possible for the intense sunlight to strike 
the bases of the young flax plants with the least interference from weeds 
and other flax plants. Likewise, in a series of experimental plats at 
Fargo, N. Dak., in 1917, in which the stand varied greatly because of 
variation in germination of seed, it was noted that the most flax 
canker resulted where the stand was thinnest. The results of these 
three sets of observations are summarized in Table 1 . 
Table 1. — Summary of field observations of heal canker of fiax on plats and under field 
conditions in 1917. 
Location and field condition. 
Mandan, N. Dak.: 
Nursery plats 
Rotation plats 
Farms: 
Breakiiig (thin stand; few weeds) 
Old land (thick stand; many weeds). 
Fargo plats: 
Thin 
Canker under different conditions. 
Tliin stand; no weeds. Thick stand; weedy. 
stand.. 
Thick stand. 
Canker abundant. 
Canker abundant . 
Canker abundant . 
Canker slight or absent. 
Do. 
Do. 
These observations show that flax canker occurred most abun- 
dantly where the bases of the young flax plants and the adjoining 
soil were exposed to intense sunlight, on account of the thin stand 
and the absence of weeds. 
