Fiber Plants 351 



and South Dakota. On such soils flax plants are attacked at 

 any age, and die early or late according to the time and in- 

 tensity of the infection. Many of the plants are killed before 

 they appear above the surface of the ground. Such field 

 spots become centers of disease; they enlarge throughout the 

 summer, and new plants sicken, wilt, and die around their 

 margins, finally giving the entire field a spotted appearance. 

 Young plants wilt suddenly and dry up, or decay if the 

 weather is moist. Older, woody plants become sickly and 

 weak, turn yellow, wilt at the top, and die slowly. Such 

 plants are easily pulled up, owing to their decayed root 

 system. 



Many of the roots of diseased plants are dead and have 

 a characteristic ashen-gray color. If the plant is attacked 

 late in the season, this gray color may be limited to one side 

 only of the taproot. In such cases the leaves and branches 

 on the affected side are blighted. If the disease is carried with 

 the seed into healthy soil, only a few plants may l^e attacked 

 during the first year, and such plants may be very unevenly 

 scattered throughout the field and escape notice until late in 

 the season. 



If the weather favors the disease, each new area of infesta- 

 tion may increase sufficiently to reach plants in several 

 adjacent drill rows. These infested areas are nearly al- 

 ways circular, and enlarge each year that flax is grown 

 thereon. Such a spot 1-2 m. in diameter the first year 

 may become 2-3 m. the second year. Thus only a few years 

 are required for the disease to gain complete possession of a 

 field. The fungus not only persists in a field not sown to 

 flax, but the disease areas may even enlarge when no flax is 

 present. When soil is once infested, no way is known to 

 render it again suitable for flax culture. 



This is essentially a soil disease, and it is spread in the 

 ways suggested under soil diseases, notably by soil particles, 

 drainage water, and especially by straw of diseased flax which 

 may get into the manure. The chief agent of dissemina- 

 tion, however, is the seed. In threshing, the spores of the 



