Brown. — Studies in the Physiology of Parasitism. IX. 295 
A number of pure chemical substances were also tested, including 
various esters of ethyl alcohol and several essential oils. The following is 
an experiment with ethyl acetate : In each of four 3-litre containers 50 c.c. of 
water was placed and in order o, 1, 2, and 10 drops of ethyl acetate added. 
The slides with spore drops were then put in and the lids of the containers 
immediately replaced. After two days the following figures for germination 
were obtained : 
Control. 1 drop Eth. Ac. 2 drops Eth. Ac. 10 drops Eth. Ac. 
0.36 1.82 1.54 0.46 
/ 
These results indicate a distinct optimum effect, as was to be 
expected. 
A rough comparison was made of several ethyl esters by testing the 
effect of a few c.c. of a saturated watery solution of each and of a tenth 
dilution of the same on the germination of Botrytis in Petri dishes. In all 
cases inhibition was shown in the presence of the saturated solutions, while 
stimulation appeared over the tenth-saturated solutions of ethyl acetate, 
malate, and citrate. In presence of even the dilute solution of ethyl oxalate, 
complete inhibition was still shown. 
Any further comparison was not attempted, as obviously that would 
require a long investigation of itself. Nevertheless, these experiments show 
distinctly that the effects recorded earlier in this paper for plant tissues can 
be paralleled by the use of volatile organic reagents alone. 
As good stimulation had been obtained with leaves of Eucalyptus and 
Pelargonium , tests were made with the oils of eucalyptus and geranium, 
chiefly with the former. Though several experiments were made with 
different amounts of oil, nothing in the nature of stimulation has yet been 
seen with either of these oils. Even one drop of oil in a large 3-litre vessel 
is sufficient to inhibit spore germination. With water that has been shaken 
up with the oil and then diluted to various degrees, no definite stimulation 
has been seen at any point. It may of course be difficult to arrive at the 
suitable concentration, as the stimulative effect might only obtain over 
a very narrow range of concentration, but it is clear that with oil of 
eucalyptus stimulation is difficult to obtain, if it can be obtained at all, 
whereas good stimulation has. always been obtained with Eucalyptus leaves, 
as witness the experiment quoted on p. 293. It is not, of course, at all 
certain that the stimulating principle in Eucalyptus leaves is the so-called 
oil of eucalyptus at all. It may quite well be some other volatile substance 
present in the plant. 
Oil of cloves was also tested, and it appeared that when present in very 
small amount it was highly toxic to fungal spores. 
A fuller account will now be given of the blotting-paper effect which 
has already been several times mentioned. The magnitude of this effect 
