47 o 
Journal of Agricultural Research 
Vol. XXVII, No. 7 
A consideration of the totals for all temperatures and all humidities 
shows, on the whole, a tendency toward progressive decrease in the relative 
number of spores which germinated, but at 75 per cent relative humidity 
there was apparently no significant decrease in the amount of germina¬ 
tion during the experiment. 
In the 37 0 C. series, a few spores germinated within a range of from o 
to 50 per cent relative humidity after exposure for five months from the 
commencement of the experiment. 
When tissue containing fresh spores was exposed to the relative humidity 
series, it was found that drying over concentrated sulphuric acid at first 
accelerated the germination of a large number of spores, but constant 
exposure to this condition eventually inhibited germination. Spores ex¬ 
posed to the medium relative humidities reached their maximum germi¬ 
nation capacity later than did those in the low relative humidities, but this 
capacity for germination was retained for over six months in a manner 
similar to that observed in Table VI. 
It was observed also that the spores from each of the three lower 
temperature ranges (5 0 to 26.5° C., inclusive), which had been kept for 
several months in the 50 to 75 per cent relative humidity series, fre¬ 
quently began to germinate three days after their transference to distilled 
water at 22 °. Plant tissue subsequently was added to the water con¬ 
taining these spores just as in the other instances in order to obtain 
comparative readings throughout. However, it appears that exposure 
of the spores to the above-mentioned relative humidities causes a change 
in their physiological constitution, which is apparently similar in some 
respects to that induced by the various stimulatory agents described 
above. 
It is obvious that a number of limitations are to be noted in the ex¬ 
periments just described. It may well be expected that there are differ¬ 
ences in the maturity of spores in the various leaf sections, and possibly 
also inherent individual differences in spores which are considered equally 
mature, for spores produced under varying environmental conditions 
may respond differently to the influence of the controlled environmental 
conditions of such an experiment. The question arises, also, as to 
whether the undisturbed spores of the sorus are completely affected by 
the relative humidity to which the tissue is subjected. Exposed spores 
undoubtedly would be more readily subject to this influence, although 
under natural conditions they often may remain in the tissue for con¬ 
siderable periods. In making the germination tests, it evidently is not 
practicable to maintain absolutely uniform conditions throughout. 
However, it is believed that a consideration of the consolidated totals of 
percentage germination at each relative humidity indicates that, although 
the extreme limits have not yet been determined, medium relative 
humidities favor the longevity of the spores. 
INOCULATION AND INFECTION 
SEEDLING INFECTION 
Me Alpine ( 29) first reported inoculation experiments with this fungus. 
Infection occurred when spores were dusted on the seed and also when 
clean seed was sown in infested soil. There is no available information, 
however, as to the actual conditions under which infection may occur. 
Reference frequently has been made to the fact that seedlings are sus¬ 
ceptible to certain smut fungi only during a very limited period. 
