Brown. — Studies in the Physiology of Parasitism. IX. 297 
were added to the blotting-papers in a series of Petri dishes, by which 
means it was established that at a dilution of 1 in 100 less retardation was 
caused than with blotting-papers which had been left wet with water for 
a week. At the end of the germination test, the addition of permanganate 
solution showed no definite reaction for hydrogen peroxide in the latter 
case, whereas a distinct rapid decoloration was shown in the former. The 
retarding effect on spore germination cannot thus be due to hydrogen 
peroxide. 
The retarding effect of blotting-paper is not demonstrable when small 
traces of nutrient are present in the germination drop. The following test 
of germinations in various dilutions of turnip extract, carried out in Petri 
dishes with and without blotting-paper, illustrates this point : 
Table 
VII. 
T . E ./ i , 000. 
TE ./ s , 000. 
T E.f 25,000. 
T . E ./ 100,000 
Water 
No B.P- 
long 
3 * 7<5 
3 ’ 12 
2.88 
2.52 
B.P. 
long 
4-12 
0.74 
0*20 
0*20 
The effect, therefore, is only demonstrable in sowings in water or in 
extremely dilute nutrient. 
Discussion. 
The experiments described in the present paper point to a marked 
degree of sensitiveness on the part of fungal spores to the presence of traces 
of volatile organic substances in the atmosphere to which the spores are 
exposed during germination. Such stimulation is not large absolutely, and 
accordingly is only in general demonstrable when the spores are placed in 
conditions of very limited food supply, as for example in pure water. The 
behaviour of fungal spores in water is a matter of considerable importance 
in the study of pathology. The bearing of the results of this paper on 
such study may now be indicated. 
Germination studies are in many cases carried out in an incubator, and 
usually in the presence of other fungal cultures. Every one who has worked 
with fungi knows the characteristic ‘fungous’ odour which clings to an 
, incubator which is in constant use. In the case of germination studies in 
which the ordinary cultural media are used, any effect arising from the 
atmosphere would probably be negligible ; when, on the other hand, one is 
dealing with germinations in water it is not at all certain that the effects 
produced by these volatile substances could be ignored. As a case in 
point, we may adduce the effects produced by blotting-paper already 
described. Here there seems no doubt that the effects in question are 
produced by the action of some organisms growing on the moist paper and 
giving off some volatile organic substance deleterious to germination. 
In carrying out studies of germination in water, one should therefore 
