Brown . — Studies in the Physiology of Parasitism. VIII. 109 
the investigation it is of no importance, as the slight gain in conductivity 
is not accompanied by any increase in the capacity to stimulate 
germination. 
The failure of Botrytis spores to germinate in the tap-water (hard) is 
worthy of note. 
The correspondence between conductivity and amount of germination 
was shown also for drops laid on petals of Poppy, Iris, Petunia, Geranium, 
and Rose. 
Exosmosis from other Plants. 
The results as detailed in the case of Cereus are paralleled in the case 
of other plants. A brief summary of the type of results obtained may be 
given here. 
Petals of Phyllocactus gave figures for conductivity and germinative 
capacity of about the same magnitude as those of Cereus. They are, 
however, much inferior to the latter from the point of view of infection 
studies. 
Petals of Tulip (var. ‘Keizer Kroon’), Cydonia, Sweet-pea, Petunia, 
and Geranium give in general smaller conductivity figures. The effect on 
germination is, however, quite distinct. 
Petals of Rose, Viola, Lilium, Begonia, Gloxinia, and Tulip (var. 
‘ Darwin J ) give low conductivity figures and only very slight effect on 
germination. 
The last-mentioned petals have the common feature of being difficult 
to wet. This is specially marked in petals of Viola, where the drops 
maintain an almost spherical shape and can hardly be said to be in contact 
with the petals at all. In the case of Begonia (female flower) it was 
noticed that drops on the petals showed very incomplete wetting with low 
conductivity and low germination figures, whereas on the ovary wings much 
better wetting took place, with a corresponding increase in the figures 
obtained for conductivity and germination. The same applied to the lobes 
of Gloxinia petals as compared with parts of the corolla lower down. It 
is highly probable that if a suitable method could be found for overcoming 
this difficulty of non-wetting it would be found that the amount of exosmosis 
and the corresponding capacity of the drops to stimulate spore germination 
would in all cases be considerably increased. 
Exosmosis in Relation to Attack. 
Some experiments will now be described in which the fact of exosmosis 
of nutrient into the infection drop is brought out by an examination of the 
progress of attack. This method is based on a comparison of the time 
required to effect attack when the spores are sown in water with that in the 
case in which the spores are sown in nutrient extract. 
