292 Brown . — Studies in the Physiology of Parasitism . IX. 
in all cases. This experiment proves conclusively that the carbon dioxide 
evolved by the apples is not the factor affecting the germination. 
An experiment in which the germination in air was tested against that 
in 3 per cent. C 0 2 artificially made up gave the following result: 
In air Germination = 0*44 
In 3 per cent. C 0 2 „ = 0-30 
This further confirms the foregoing result. 
A similar conclusion was reached for the retarding effect shown by 
potato tissue. 
The stimulating effect of apple can be obtained with slices, with’bruised, 
or with unbruised whole apples. As far as could be seen, the- effect of the 
last mentioned was just as great as that of any of the others. The conclu- 
sion is thus reached that healthy unbruised apples can markedly stimulate 
spore germination in their vicinity. 
In some tests an attempt was made to vary the amount of stimulation 
by using 1, 2, 5, &c., slices of apple, and as the final member of the series 
a considerable amount of pounded apple tissue. A distinct optimum effect 
was in some cases observed, that is, reduced germination was again met with 
in the last case. This optimum effect will be alluded to later in dealing 
with stimulation by ethyl acetate. In the present case it was not certain 
that fermentation in the pounded-up tissue may not have played a part in 
the result. 
The following experiment, carried out in large containers, may be cited 
as confirming a statement already made, viz. that the effects described 
are more clearly discernible with somewhat feebly germinating spores than 
with vigorous ones. 
Apple. 
Absent 
Present 
Table IV. 
Spores.. 
Old 
Younw 
Old 
Young 
Germination. 
061 
1.50 
2-43 
3.28 
The ratio of stimulated to control spores is 4-0 for the old spores and 2*2 
for young spores. The effect of stimulation is thus more striking in the 
former case. 
The following somewhat detailed experiment may be quoted as 
illustrating among other things the retarding action arising from blotting- 
paper. The plants tested were : bruised leaves of Eucalyptus, slices of 
apple fruit and of potato tuber, and strips of rind of orange. Half the 
Petri dishes (all of which had been strongly heated in the oven) had 
blotting-paper in their lids. This had been kept wet for seven days before 
the plant tissue was put in. The other half of the Petri dishes were without 
