Feb. 9, 1924 
Effect of Fertilizers on Stem Rust of Wheat 
373 
The calculated odds for height of plants of Marquis are 20.7 : 1 in 
favor of the series receiving nitrogen. (Table XIII.) These odds are 
hardly great enough to be considered significant. The differences between 
the individual plats, however, are quite consistent, and the average 
height of plants on the plats receiving nitrogen is 39.8 inches and for 
all others it is 36.2 inches. 
The calculated odds for percentage of crude protein (Table XIV) in 
the seed of Marquis is 21.5 : 1 in favor of the series receiving nitrogen. 
These are only fairly significant; but here, too, as for height of plants, 
the differences between the individual plats are small but quite con¬ 
sistent. The average percentage of crude protein for all plats receiving 
nitrogen is 15.8 compared with 12.9 per cent for all other plats. 
On the plats at the Anoka farm in 1917 (Table XV) the calculated 
odds for rust on Marquis are only 1.6 : 1 in favor of the series receiving 
nitrogen. For yield of grain, however, the odds are 45.3 : 1 in favor 
of the series receiving nitrogen. This experiment was made on a light, 
sandy soil, and the application of sodium nitrate was very beneficial. 
The average yield per acre for all plats receiving nitrogen is 27.4 bushels 
and that of all other plats is 16.4 bushels. 
Unfortunately, the experiments in 1915 and 1916 with barnyard 
manure were not laid out so that it would be feasible to arrange the 
plats in series and calculate odds for significance of difference in results. 
In 1915 the average percentages of rust for Bluestem and the hybrid 
on the manured plats was 83 and 38.4 per cent, respectively, compared 
to 70 and 33 per cent, respectively, for the controls. These rust percent¬ 
ages, which were taken at the time of maturity of the last plat to ripen, 
appear to indicate significant differences. There is a direct relation 
to the time of maturity, however, as is illustrated in Tables IX and 
XVII where, on a given day, say the date of maturity of the first control, 
there are no differences in the rust percentages in the various plats, but 
where some of the plats remain green and exposed to infection for a 
longer period of time, their total percentage of rust infection is bound to 
increase. In 1915 the average number of days from seeding to maturity 
was 114.6 compared to the controls with an average of 102.7. 
GENERAL CONCLUSIONS 
In discussing the effect of fertilizers on the susceptibility of wheats 
to Puccinia graminis , it is necessary to consider what is meant by this 
susceptibility. Plants may be physiologically resistant, or morphologi¬ 
cally resistant, or they may merely be disease-escaping. That there is a 
true physiologic or protoplasmic basis for resistance to P. graminis , 
probably none will deny. It is well known that this is a genetic character 
comparable with other hereditary characters. The results of field 
experiments and observations suggest also that plants sometimes may be 
resistant on account of morphologic characters. Certainly, plants 
with a large amount of woody tissue are not likely to be so severely 
rusted as are those with a larger proportion of succulent tissue because 
the rust fungus requires the latter for growth. But this morphologic 
resistance is quite different from true protoplasmic resistance; it is only a 
mechanical limitation on the spread of the rust mycelium. Under normal 
conditions, in some varieties, it undoubtedly is due to inherited genetic 
factors, while in other varieties it may be due to environmental condi¬ 
tions. It also is well known that early maturing varieties may ripen 
