Brown . — Studies in the Physiology of Parasitism . VIII. 1 1 7 
Discussion of Results. 
It would be prematur.e, with the data at present available, to try to 
estimate the significance of the foregoing results in relation to the 
physiological processes of infection. The present paper deals mainly with 
floral organs, and thus touches only a small and unimportant part of the 
field of parasitism. As has been already stated, the difficulty met with 
in the treatment of foliage leaves lay in the fact that no satisfactory 
parasitism of the leaves investigated could be brought about by Botrytis. 
Thus the examination of foliage leaves according to the method of the 
present paper could be carried out only in its negative aspect. With a view 
to the further development of this problem an investigation of some fungus 
more suitable for this purpose than Botrytis is projected. 
In all the cases examined it has been found that drops of water when 
laid on the surface of plant structures show an increase of conductivity, 
which increase has been found in a number of instances to be accompanied 
by an increased capacity for stimulating germination. The increase of 
conductivity, due to leaching of electrolytes from the plant, is in agreement 
with a large body of recent work dealing with the permeability of the 
living cell-membrane to electrolytes (and other simple solutes) and requires 
no further emphasis here. From the pathological point of view the essential 
point brought out is that water drops when laid on plant structures are 
altered in respect of their capacity to stimulate spore germination. Drops 
so treated show in some cases a very marked increase in this respect ; in 
other cases the effect obtained is much less ; and finally cases were met 
with in which the treatment actually reduced the amount of germination 
as compared with that taking place in the water controls. As it has been 
proved in earlier papers that the fungal spores exert no influence on the 
host previous to penetration of the cuticle, it is obvious that the preceding 
results which were obtained for drops of water laid on the plant are directly 
applicable to the infection drops themselves. The amount and quality of 
the substances diffusing into the infection drop must obviously exert an 
important influence on the behaviour of spores. Where the substances 
diffusing out from the plant have a marked stimulating effect on germination, 
the fungal spores when sown in water will germinate as in nutrient 
and will therefore be able to attack the plant with the vigour induced 
by good nutrition. Where the substances diffusing from the plant 
are such that they exert no appreciable influence one way or the 
other on the germination of the fungal spores, the course of affairs 
will be largely dependent on the inherent vigour of the spores. If these 
are young, a certain amount of germination will take place and attack may 
in some cases follow ; if they are old (or in other ways attenuated), 
