10 BULLETIN 1210, U. S. DEPARTMENT OF AGRICULTURE. 
Volkart (384) found that the optimum temperature for spor 
germination was between 16° and 18° C. Between 18° and 20° C 
the germination began just as quickly, but was less vigorous. Above 
25° C. there was no germination, but the spores remained uninjured 
Volkart apparently did not undertake to fix the minimum. The 
figures in Table 1 are from a series of Volkart’s experiments to deter: 
mine the relative response of wheat and bunt spores to various tem 
peratures. 
Tasie 1.—Data on germination of wheat and of bunt spores, at various temperatures 
according to Volkart. 
‘Temperature. | W heat germination. Spore germination. 
5.0° to6.1°C { a DEE CONGO TOS SuULiGay, 502/54 2.0 - 4 shoe ee | A few on the 12th oar 
7 Seah og ChE EF 93 per cent on the 12th day. ........2..5....--20. | Abundant on the 15t day. 
12.0° to 12.9° © ‘61 Der cen ton thie Sth day... 2 pnp 344-2 sessed esr | Moderate on the 5th day. 
f ; Sheree oF NOU Pave nGON. Ue OL Mave tak. «sco Sembee cere. ees | Abundant on the 6th day. 
17.8° to 21.4° C { 8 per cent.on the 2d day..:-..-22..--.2Reees oes ' Abundant on the 5th day. 
; yy gt ee ee \\99 per cent on the 6th day... s....... 6. ..-02-csee- 
28. 3° to 33.6° C i Siper.cent'on the 2diday.An.2.. WALA. if. None. 
§ a “vos=ss*""1\98 per cent on the 8th day.....--...-----++---+- 
33.1° to 37.2° Us......... 463 por Centon fhe 30 GBy-..<- 4... 5.5. --bact- ove Do. 
63 per cent on the 12th day. ...:.-.....-....-.... 
Volkart (384), contrary to the view held by Tubeuf (372, 374), 
concludes that the lower the temperature of the soil the greater the 
liability to infection. | 
Hecke (1/47) conducted careful experiments with spring sowings 
in 1907 and 1908, extending from March 3 to May 21, during which 
time he kept a continuous record of soil temperatures. He states 
his conclusions as follows: ‘“‘In case of bunt, the view that the degree 
of infection is in inverse proportion to the temperature is without — 
doubt correct.” He also notes that this would indicate early fall 
sowing, which is generally known to be less infected than late. Hecke, 
however, does not believe that the temperature influence is limited to— 
the germination period. He further states that there are three ways 
in which temperature may exert an influence: (1) It may affect the 
germination of the spores and the seed; (2) it may lengthen or shorten 
the duration of susceptibility to infection; and (3) it may limit or 
proot the ability of the fungus to reach the growing point of the 
ost plant. ) - 
The field experiinents of Munerati (283, 284, 285) furnished fur- 
ther support for the views of Volkart and Hecke. All his seedings 
showed a reduction of bunt with rising soil temperature, but in his 
case, however, the soil temperature can be inferred only, as he de- 
pends on the air-temperature records taken at a neighboring weather 
station. | 
Miller and Molz (275) also investigated this question (see table 2 
for their results). Their temperature observations are open to the 
same source of error as those of Munerati, i. e., they are air tempera- 
tures from a weather station, the distance of which from the 
experimental plat is not stated. 
