spore Germination of Ustilago Avenae 
579 
May 19. X923 
with the views of Tubeuf {22), as given in the first of this paragraph. 
Also, Eriksson (7) considers that damp, warm weather during the sowing 
favors infection. Heald and Woolman (jo) have found that a range of 
temperature between 40® and 65® P. during the germination of wheat is 
more favorable for bunt infection than either a higher or a lower tempera¬ 
ture. It is of interest that this range includes the minimum and the 
optimum for the germination of bunt spores as given by Hecke (12). 
There are several nontechnical bulletins which mention the importance 
of temperature. Heald (9), in advising the early or late sowing of 
wheat, shows that during August not only is there a comparatively small 
number of smut spores in the soil, but that also the soil temperature is 
generally too high for optimum infection; and by the end of October or 
the first of November, not only has mudi of the wind-blown smut ger¬ 
minated, but also there is the frequent occurrence of a soil temperature 
too low for ready infection. In a similar publication, Heald and Zundel 
(ii) state that early seeding of oats results in the minimum amount of 
smut. 
DURATION OR SUSC^PTIBIWTY OR HOST PI.ANT TO INRRCTION 
Volkart {23) was the first to emphasize the fact that low temperature 
may prolong the infection period. He states that witib oats and wheat 
the slower Qie initial stages of growth, the more abundant and severe 
will be the infection. However, extremely low temperatures may retard 
not only the germination of the seed but also may retard even more the 
germination of the smut spores and thus remove the danger of infection. 
This point is more clearly set forth by Hecke {12), The latter's experi¬ 
ments dealt with the bunt of wheat which he found occurred most abun¬ 
dantly among plants which had passed their early stages during the low 
temperatures of late fall and early spring. The temperature of the first 
five days seemed decisive. That low temperatures at that time caused 
increased infection he lays in the main to the prolonging of the infection 
period, although he also discusses what he considers a greater ease with 
which the fungus may reach the growing point. In comparing oat 
smut with bunt in this temperature relation, he considers the low tempera¬ 
ture not only as a factor retarding the development of the oat seedling, 
but also as one delaying the germination of the smut spore. The possi¬ 
bility of this being true is substantiated by the cardinal points of tempera¬ 
ture. These, according to his citations, are as follows: For oatSj 
minimum 4° to 5° C., optimum 25°, and maximum 30°; for oat smut, 
minimum 5® to 11° (9^^), optimum 22° to 30°, maximum 30"^ to 35®; 
for wheat, minimum 3° to 4.5®, optimum 25^, maximum 30® to 32°; 
and for bunt spores, minimum less than 5®, optimum 16° to 18®; maximum 
less than 25° 
Munerati (19) emphasizes the importance of the duration of the 
infection period for heavy bunt infection. He states: 
The faster the first phases in the evolution of the life of the seedling are passed through, 
the more completely is it able to escape attack by Tilletia, and vice versa. 
He comes to such conclusions as the result of experiments recorded in 
two publications (18, 19). 
It is obvious that a deeper sowing of seeds might have the effect of 
prolonging the infection period in a way similar to a low temperature. 
Jones (j6) makes note of the factor of the depth of seeding. 
Kirchner's (17) conception is at variance with that of Volkart (2j), 
Hecke (12), and Munerati (ip). Kirchner, also working with bunt, says 
