- FOOT-ROT DISEASES OF WHEAT IN AMERICA 15 
that fertilizers containing potassium tend to reduce their severity. 
Hori (31) states that take-all is most severe when applications of 
nitrogenous fertilizers have been made and when the three essential 
elements are unbalanced. Other investigators claim that nitrogen- 
ous fertilizers intensify foot-rot; still others, that they tend to con- 
trol it. It is not clear in all cases, however, that these investigators 
are dealing with Ophiobolus graminis. Rosen and Elliott (67) 
report that during the one year their experiments were conducted 
the amount of take-all was greatly reduced by the use of a complete 
wheat fertilizer and farm manure. 
In general, it seems that the phosphate fertilizers, such as acid 
‘phosphate, Thomas phosphate, and superphosphate of lime, tend to 
reduce take-all, whereas nitrogenous fertilizers tend to increase the 
severity of the disease. While further studies must be made before 
the exact influences of these fertilizers on take-all will be known, it 
would seem apparent from results now in hand that the success of 
these materials is tied up with some other influencing factor or set 
of factors. 
There are several statements in the literature cited concerning the 
effect of lime on the development of take-all, but, as Brittlebank (77) 
points out, it is not definitely known whether the disease is favored 
by an acid or an alkaline soil. In some of Brittlebank’s field ex- 
periments he found that applications of lime to the soil increased 
the infestation of take-all, but he was not inclined to draw definite 
conclusions from these experiments on account of their short dura- 
tion. Kirby (37) studied the influence of various hydrogen-ion 
concentrations on the growth of Ophiobolus graminis in pure culture 
and reported that alkaline media were most favorable. He also 
carried on pot experiments in which he made applications of lime 
and sulphur. Although these were rather hmited, Kirby concluded 
that lime favors development of the disease. 
Davis made preliminary studies on the growth of several strains 
of Ophiobolus. graminis on artificial media varying in hydrogen- 
ion concentrations, and his results indicate that growth is favored 
by a slightly acid substrate. Kirby and Davis did not follow exactly 
the same methods, in that Kirby’s cultures were grown in the dark 
and those of Davis in the ight. Also, Davis’s cultures were grown ~ 
for a longer period. Webb and Fellows’? took up this problem 
in a rather comprehensive manner in order that the seeming dis-< 
crepancies in the results of Kirby and Davis might be harmonized 
if possible. Their results indicate that the type of medium used and 
the method employed in its preparation have much to do with the 
influence of the hydrogen-ion concentration on the growth of the 
fungus. They have shown that under certain conditions the fungus 
is favored by an acid medium, whereas under another set of condi- 
tions growth is favored by an alkaline substrate. It appears that 
the fungus thrives over a rather wide range of acid and alkaline 
reactions when grown in certain media. This relationship makes it 
appear that the control of take-all through attempts to adjust soil 
reactions is likely to be very uncertain. 
Such disinfectants as copper sulphate, corrosive sublimate, lime- 
sulphur, and sulphuric acid have been applied to infested soil with 
10 Webb, R. W., and Fellows, H. Growth of Ophiobolus graminis Sacc. in Relation to 
Hydrogen-ion Concentration. (Unpublished manuscript.) 
