502 FROMME: THE CULTURE OF CEREAL RUSTS 
Morgenthaler (25) finds that mechanical injury of the leaves 
of the host favors teleuto as compared with uredo formation in 
the case of Uromyces Veratri. Tischler (36) found that shoots of 
Euphorbia Cyparissias infected with Uromyces Pisi became free 
from the rust mycelium when grown in a warm (25-27° C.) 
greenhouse. 
Many factors doubtless influence the germination of rust 
spores. They frequently germinate in a ‘few hours after being 
placed in water, as noted by de Bary. Often, however, though 
collected fresh, they fail to germinate for no apparent reason. 
This “capricious”’ germination has been noted by a large number 
of careful observers, and Eriksson, because of this uncertainty, 
does not consider the aecidiospores of the rusts of the cereals im- 
portant factors in their dissemination. Schaffnit (31) explains 
this ‘‘capricious’”’ germination on the ground that unless the 
spores are mature internally before detachment from their stalks 
they are incapable of germination. Complete maturity is at- 
tained only at a sufficiently high temperature (20°-25°) in an 
atmosphere calm enough to prevent their premature detachment. 
These conditions are not always realized in nature, hence the 
lack of uniformity in the results of germination tests. 
Freeman (13) and Klebahn (19) both have found that spores 
which germinate poorly in water may produce an abundant 
infection on the host, and therefore argue that germination tests 
are not conclusive unless conducted on the host. Klebahn states 
that aecidiospores of Peridermium Strobi germinated slightly 
or not at all in water, very vigorously on the Ribes host and less 
vigorously, but abundantly, on a decoction of Ribes. Sappin- 
Trouffy (30) likewise noted a marked difference in the germination 
of aecidiospores of Coleosporium Senecionis in water and in a 
decoction of Senecio vulgaris. Schaffnit (31) on the other hand, 
obtained no increase in host decoctions over the germination 
in water nor any effect attributable to a mechanical excitation 
by the substratum. Marshall Ward (37), was unable to find any 
effect of raw or cooked extracts of various bromes on the germina- 
tion of the uredospores of Puccinia dispersa. 
The effect of various chemicals on rust spore germination has 
been investigated by Wiithrich (40) and Carleton (6). Wiithrich 
