214 
Journal of Agricultural Research 
Vol. XXVI, No. S 
It will be noted that the high rainfall during the growth periods of 
the later sowings in 1921 tended to raise the disease curves, but in the 
case of the last sowing it would seem that the decided drop in tempera- 
ture had more influence on the disease than the marked rise in the soil 
moisture, since the disease curve went down at this time. 
While it was not possible under the prevailing conditions to obtain the 
data on the several plots at exactly the same interval after seeding, 
this was done at intervals sufficiently close, as shown in Table IX, 
practically to eliminate the time element, except possibly in the case 
of the seedings made on October 19 and November 11. In these cases, 
however, the increased time period should have increased infection, 
but it did not seem to influence the results seriously. 
In general, the results from the field experiments are in line with those 
obtained in the constant temperature experiments conducted in the 
greenhouse. This seems to strengthen the idea that the results of the 
latter experiments are a safe index to the soil temperature influence 
on the phases of the Helminthosporium disease under consideration. 
DISCUSSION 
While the foregoing results are considered as preliminary in nature, 
it seems evident that soil temperature and soil moisture are important 
factors in connection with the development of the Helminthosporium 
disease on the subterranean parts of spring and winter wheat and spring 
barley. Whether or not these are the mosit important environmental 
factors can not be determined from the data at hand. In this con¬ 
nection it is of especial interest to note that Hungerford (5) has observed 
severe Helminthosporium injury to wheat plants in Idaho only in the 
dry-land regions; and it is of further interest to note that he considers 
the trouble to be favored by a cold, wet spring followed by hot, dry 
weather. Obviously, these observations involved many variable factors, 
the relative importance of which is not known at this time. 
Other factors than temperature and moisture undoubtedly influenced 
the development of the Helminthosporium disease. This conclusion 
is supported by the fact that there has been some shifting in the tem¬ 
perature optima of the several controlled experiments presented in this 
work. Dickson (4) has noted that light exerted an influence on his 
soil temperature experiments with the Fusarium blight of wheat, and it 
may be that there was such an influence on the writer's results with the 
Helminthosporium disease. As yet, however, too little evidence is in 
hand to warrant a direct statement on this point. 
By way of comparison it is of interest to note the differences in response 
between the Fusarium and Helminthosporium seedling diseases on 
wheat. Results obtained by Dickson (4) in his study of Fusarium blight 
show that Turkey wheat (winter) is attacked, on the average, more vig¬ 
orously at 28° C., whereas the writer’s results with the Helminthosporium 
disease show that Harvest Queen (winter) wheat is attacked, on the 
average, more severely at 32 °. In the case of Marquis wheat the results 
are the more striking in that Dickson’s average data show a bimodal curve 
with the optimum at 20°, whereas the same variety shows a much higher 
temperature optimum (28°) for the Helminthosporium disease with no 
indication of bimodal tendency in the average data. A few of the writer’s 
experiments with the Helminthosporium disease have shown a very 
