344 
Journal of A gncultural Research voi. xxvn, no. 6 
sium and phosphorus salts tend to decrease it. Some investigators, 
notably Comes, apparently attribute the effect principally to changes 
in the chemical composition of the plants; others, such as Schindler 
(26, p. 168), Russell (25), and Miyake and Adachi (79) think the effect 
is rather on the mechanical composition of the cell walls. Schindler says 
that acid phosphates seem to cause the development of stronger tissues 
(“strammeres Gewebe”). Russell concludes that the walls of plants 
fertilized with excess nitrogen are thinner than they normally would be, 
and parasitic fungi therefore can penetrate more easily. Miyake and 
Adachi agree with Russell regarding the effect of nitrogen, and they 
report that potassium fertilizers strengthen the cell walls and thus in¬ 
crease resistance. Still others, especially Gassner (10), Freeman and 
Johnson (8), Stakman and Aamodt {32), and Armstrong (2), suggest 
that the effect of fertilizers is at least partly indirect. 
Hurd’s results (1 3) do not support the views of Comes that acidity of 
the host plant is the determining factor in resistance. She found no 
positive correlation between hydrogen-ion concentration and resistance. 
Neither could Hursh 5 find any correlation between sugar content of 
different varieties and the resistance to Puccinia graminis . On the 
other hand, there is some evidence that fertilizers may alter the structure 
of the host sufficiently to account partly, at least, for differences in the 
resistance of the same variety grown under different conditions. 
That fertilizers may cause an apparent change in resistance by in¬ 
fluencing rate of growth, density of stand, date of maturity, and yield 
can hardly be questioned. 
OBJECTS OF THE INVESTIGATION 
The objects of the investigation were: 1. To ascertain whether natural 
and artificial fertilizers alone and in various combinations, directly or 
indirectly, affect the degree of susceptibility of susceptible and resistant 
varieties of wheat to Puccinia graminis and P. triticina; 2. To ascertain 
what effect fertilizers have on the density of stand, the succulence of the 
plants, the degree of lodging, the date of maturity and similar characters 
which might indirectly influence the development of the rust; 3. To de¬ 
termine whether the same amount of rust will produce different degrees 
of injury when the plants are grown in different types of soil; 4. To de¬ 
termine whether plants receiving excessive nitrogen fertilization are 
especially liable to rust injury. 
Attempts were made to predispose plants by means of barnyard ma¬ 
nure, by growing them on clover and alfalfa soils and by adding nitrates 
directly to the soil. It was desired also to find out whether phosphates 
and potash could counteract the effect of large amounts of nitrogen and 
whether a combination of fertilizers could be found which would enable 
the plants to yield well in spite of rust. While the primary object was 
to determine, for practical purposes, the effect of normal amounts of 
fertilizers on the severity of rust attacks, attempts also were made to 
ascertain the effect on rust resistance of excessive amounts of fertilizers. 
As the work progressed, it became increasingly evident that it would be 
necessary to secure data on the effect of fertilizers on density of stand, 
succulence, degree of lodging, date of maturity and similar characters 
which indirectly might affect the development of rust without necessarily 
changing the actual resistance of the plants. 
6 Unpublished results. 
