4 BULLETIN 765, U. S. DEPARTMENT OF AGRICULTURE. 
The symptom of this disease is, then, a decay of the root system, 
resulting in a stunting of the plants, roughly proportional to the ex- 
tent of th e decay in the roots. The effect of the disease on the root 
system and the growth of the plant is shown in figure 1. Very fre- 
quently the plants make no growth during the season, on account of 
this disease. Curiously enough, root-rot rarely kills the plants in the 
field. Aside from becoming stunted and yellow, they may show wilt- 
Fig. 1.—Plants of Burley tobacco grown on “‘ tobacco-sick ’’ soil (A) and in soil free from 
disease (B), showing the relative number of roots. These plants were grown under 
identical conditions, except that the soil in which plant B was grown was Sterilized, so 
as to kill the parasites causing the disease. , 
ing, even in very moist soils, on days when tobacco in healthy soil 
and other crops show no wilting. The depleted root system is not 
able to take up water as fast as the leaves lose it, causing temporary 
wilting. It is not, however, a typical wilt disease, since the leaves 
do not remain wilted. Crops with root-rot suffer from “ drought,” 
therefore, very much more quickly than healthy crops. 
The importance of this disease is shown by the fact that careful 
observations over a considerable part of the tobacco-growing sections 
