1 1 8 Brown . — Studies in the Physiology of Parasitism. VIII. 
germination will not take place and no attack will be possible. Lastly, 
where the substances diffusing from the plant are such as to inhibit the 
spore germination, it is obvious that no attack can take place in the 
circumstances. 
It is well known that in some cases immunity is in no way related to 
considerations such as those outlined above. Thus in some of the Rusts 
it has been shown that both immune and susceptible varieties of the host 
are actually penetrated by the fungus. The differential effect appears only 
after penetration has taken place, inasmuch as further growth of the fungus 
is inhibited in the case of the immune variety, whereas it continues in the 
other. Here, therefore, the immunity or susceptibility of the host is not due 
to conditions prevailing in the infection drop, but to different and more 
complex relationships between host and parasite which come into play only 
after penetration has taken place. Nevertheless, there are cases where 
attack is determined by the conditions prevailing in the infection drop. 
The parasitism of the Bean leaf by Botrytis. is a case in point. Here the 
incidence of attack is dependent on whether sufficient nutrient is present 
in the infection drop to enable the fungus to germinate and penetrate the 
cuticular layer. If nutrient is present, attack takes place with readiness ; 
if no nutrient is present, the attack fails. It is to parasitism of this type 
that the present results apply, and in which the methods of investigation 
outlined above may prove of value in determining just why attack fails in 
some cases and why it succeeds in others. 
Summary. 
... 
i. Drops of distilled water which have lain on the surface of leaves 
and petals of a number of plants show increased conductivity as compared 
with the original distilled water or with water which has lain for an equal 
time on glass slides. 
1 . This increase in conductivity is accompanied in many cases (e. g. 
floral leaves) by a greatly increased capacity of the drops to bring about 
germination of Botrytis spores as compared with that of the original water. 
In some plants drops so treated, though showing a comparatively high 
degree of conductivity, have no greater effect on germination than drops of 
pure water. In some cases, even, the treated drops actually produce total 
inhibition of the fungal spores. 
3. In the case where increased germination effects are observed the 
amount of germination runs parallel with the conductivity. 
4. The ease or difficulty with which wetting of the plant surface 
takes place is an important factor in determining the magnitude of the 
effects produced. 
