332 DorAN: ON THE GERMINATION OF FUNGOUS SPORES 
and Durrell (7) found that when the urediniospores of Puccinia 
coronata are submerged only a small percentage of them germinate 
as compared with the number germinating when they float on 
a drop of water. 
When spore germination tests were made in non-aerated 
distilled water, the writer secured best results by sowing the 
spores on the surface of the water rather than immersing them. 
Some spores, however, will not float. According to Duggar (3) 
the spores of many of the Phycomycetes and Hymenomycetes 
usually sink. The specific gravity of the spores of several 
Hymenomycetes determined by Buller (49) were between 1.02 
and 1.21. Since some spores sink, all distilled water for germina- 
- tion studies should be aerated. 
At this point reference should be made to the injurious effect 
of the presence of fungous spores on the germination of the spores 
of other fungi. Although the injurious effect of this competition 
tween spores might be attributed to the secretion of toxic 
substances, there is little likelihood that this is the case. There 
is an indication that it is due to there being insufficient oxygen 
for all. The effect is much more marked in non-aerated than in 
aerated distilled water and is more marked in the interior of a 
rop of non-aerated distilled water than on its surface. All 
spores of Uredinales which the writer has observed germinate 
best when the drop of water in which they are contained is not 
contaminated by the presence of other fungous spores. When 
spores of Alternaria, Colletotrichum, or Cladosporium are present 
in a drop of water with the teliospores of Puccinia Malvacearum, 
the spores of the first three fungi may germinate but the telio- 
spores of Puccinia Malvacearum do not germinate, although 
check teliospores in uncontaminated drops germinate perfectly. 
When in place of Puccinia Malvacearum the conidia of Venturia 
inaequalis were used a similar result was obtained; they germin- 
ated far better when no other spores were present with them in 
the drop of water. When there is lack of sufficient oxygen for 
all, only those spores which require the least will germinate. 
It was also observed that when relatively few spores of one 
species were present in a drop they germinated better than 
when the drop was crowded. This, too, may be attributed to 
insufficient oxygen. In all spore germination studies where 
optimum conditions are desired; an effort should be made to 
exclude from the culture drop the spores of all fungi except the 
