104 Brown. — Studies in the Physiology of Parasitism. VIII. 
( Conductivity of m/ 100 KCl at 20° = 727. 1 Conductivity of the 
distilled water varied within the limits o-8-i-2.) 
Petal /. 
Petal II. 
Drop. 
Conductivity. 
Conductivity. 
1 
2-2 
4-0 
2 
2.2 
5-4 
3 
2.4 
5 * 1 
4 
5-8 
7-4 
5 
7.6 
10.3 
6 
8*5 
19.1 
In addition to observing that this rule held through- 
out all the work with Cereus, it was found in two experi- 
ments specially set up to determine this point that the 
average conductivity of 58 central drops was 47 (min. 2*2, 
max. 1 1 -2), and that of 29 marginal drops was 15*2 (min. 6- o, 
max. 39.4). 
The amount of exosmosis from the same petal in a 
given time increases day by day. This was shown by 
adding new drops to the satne places each day after the drops of the 
preceding day had been removed and examined. In such an experiment as 
this an appreciable risk of contamination of the drops by fungal spores is 
incurred, and a certain number of the petals after some days showed 
discoloured spots which were found to be caused by spores of Botrytis. 
Such petals were discarded. The following figures give the average 
conductivity (av. of 19 drops) obtained on three consecutive days from 
petals of Cereus which showed no evidence of fungal contamination on the 
fourth day. 
Average conductivity. 
1st day. 
3-6 
2nd day. 
7-8 
3 rd day. 
18.6 
The same type of result was obtained with petals and sepals of Tulip. 
In this case the rise of rate of exosmosis with time was found to be more 
gradual. 
The effect just described is due partly to ageing of the plant structure 
and partly to the fact that the method of treatment results in better wetting 
of the petals as time goes on. Experiments in which one batch of petals 
was subjected to the above day-by-day treatment, while a control batch was 
kept for the same time without the treatment, showed that the latter gave 
considerably higher figures than had been given at the commencement 
of the experiment, but not so high as those which were being given by the 
1 In arbitrary units. 
