3i4- Doran: ON THE GERMINATION OF FUNGOUS SPORES - * 
epiphytotics of fungous origin. Field experiments and. observa- 
tions on the effect of weather on diseases of plants are affected 
by a very complex set of factors. Conclusions cannot safely 
be drawn until the various factors have-been separately studied 
and such study is more easily effected in the laboratory than 
in the field. 
Factors influencing the germination of fungous spores may be 
divided into two groups, internal and external. The internal 
factors are maturity of the spore, longevity of the spore, anima- 
tion, and a poorly understood factor which may be called vitality 
of the spore. The external factors are oxygen, presence of 
moisture either in the form of water vapor or water of conden- 
sation (rain or dew), temperature, light, nutrient substances, 
toxic substances, and duration of the time period during which 
one or more than one of the factors acting jointly exert their 
influence on the spore of the fungus. 
EXPERIMENTAI METHODS 
The germination of the following fungous spores was studied: 
conidia of Venturia inaequalis (Cke.) Wint., conidia of Sclero- 
tinia fructigena (Pers.) Schrt., spores of Alternaria Solani (E. 
M.) Jones & Grout., spores of Botrytis cinerea Pers., spores of 
‘Rhizofus nigricans Ehr., aeciospores and urediniospores of 
Cronartium ribicola F. de Wal., aeciosopres of Gymnosporangium 
clavipes C. & P., and biiesiictds of Puccinia Malvacearum Mont. 
The spores of the fungi were obtained fresh from the living host 
in all cases except Alternaria Solani. Spores of parasitic fungi 
to be used for germination tests were found to be more depend- 
‘able when obtained from this source than when obtained from 
fungi growing on artificial media. A spore obtained from the 
living host is presumably possessed of its full natural vigor. 
A spore obtained from a fungus growing on artificial media may 
have been subjected to a debilitating influence, or may, on the 
other hand, have become unnaturally resistant to adverse con- 
ditions. In this connection it should be noted that Young and 
Cooper (1) found that when Glomerella rufomaculans was grown 
on agar eight to fifteen days, the Spores were more resistant 
‘to the toxic action of fungicides than when. the fungus had been 
grown on agar only four. to eight days. If fresh spores from the 
living host are not obtainable and spores from artificial culture 
must be used, it is the experience of the writer that all spores 
