Brown. — Studies in the Physiology of Parasitism . IX. 291 
amount of bruised leaf tissue much greater than was found to be sufficient 
in the case of the other plants mentioned. 
Table II. 
Leaves tested. 
Av. germ-tube. Attack of Bean leaves. 
Control o-i8 6/28 
Choisya 3-69 I 4/ I 7 
Ruta 4-42 10/11 
Amomum 0.95 17/24 
Foeniculum °'97 11/20 
Pelargonium 1-28 14/15 
Apple 2-48 16/20 
Chrysanthemum 1-20 7/14 
Broad bean 2-34 13/14 
Special attention was given in this work to volatile substances given off 
by the tissue of apple fruit and potato tuber. The former of these gives 
distinct stimulation, the latter retardation of the germination of Botrytis 
spores. 
As regards the cause of these effects, it was thought conceivable that 
they might be due to the action of the carbon dioxide of respiration. It 
was known that carbon dioxide represses germination if present in sufficient 
concentration (6). Also the possibility had to be considered that a slight 
concentration of carbon dioxide might counteract any slight alkalinity 
arising from the glass of the slides, it being known that a very slight degree 
of alkalinity had a pronounced inhibiting effect on the germination of 
Botrytis spores. The following experiment with apple slices shows that 
carbon dioxide is not the factor concerned. 
Four thoroughly washed glass containers of three litres capacity were 
used. The various liquids employed (50 c.c. of each) were placed in glass 
vessels in the bottom ; the apple slices, approximately the same weight in 
each, also in the bottom, and the slides (four in each) with the spore drops 
laid on a rack above. After two days the C 0 2 content of each container 
was analysed and the amount of germination determined in each drop. The 
following were the results obtained : 
Table III. 
Container with : 
50 c.c. H 2 0 : no apple 
: apple slices present 
50 c.c. dil. NaOH : „ „ 
50 c.c. dil. H 2 S 0 4 : „ „ 
C 0 2 content. 
Average of 4 counts of 
25 spores each. 
0.0 % 0.34 (0.14 to 0.44) 
3.3% 1.80 (1.38 to 2.12) 
o-o % 2.32 (2.18 to 2.44) 
3-i% 2.25(1.7210276) 
The amounts of germination in the last three are all of the same order 
of magnitude. The figures in brackets give the limits of variation in the 
different counts. The germination in the absence of apple is distinctly least 
