On the Physiology of Parasitism. 123 
(2) On the escape of nutrients from plant tissue into water placed in 
contact with its outer surface. 
Investigation in this connection has gone so far as to establish 
that drops of water when placed on the epidermis of plant structures 
do not remain as such but that substances diffuse out into the drops 
from the living tissue beneath. The drops may thus come to 
contain an appreciable amount of nutrient available for the 
germination of fungal spores in the drops. The method adopted 
consisted in the laying of drops of distilled water on leaf, flower, 
etc. structures for definite intervals, these drops being subsequently 
taken up and added to drops of a spore suspension in pure water. 
The effect on germination of the drops which had been on plant 
epidermis were compared with that brought about by drops < f 
distilled water which iiad lain a similar tirrn i contact w uh u as 
By this means the escape of nutrient substances con'd readily be 
detected in the case of certain living plant structures. Considerable 
exosmosis of such nutrients was shown in the case of petals of 
Cereus, Phyllocactus, certain varieties of tulip ; intermediate amounts 
in the case of sweet pea ; and small traces only in the case of 
rose petals, bean leaves, etc. The investigation was also carried 
on by an conductivity method, with confirmatory results. 
The exosmosis of nutrients from tissue could also be demon¬ 
strated in special ways. Thus it was found by the spore method 
that in Cereus petals a very considerable exosmosis took place, in 
Lilium petals, on the other hand, very slight exosmosis. It was 
found that the attack of Lilium petals by the fungus could be 
inhibited by a pressure of 15% carbon dioxide, whereas the latter 
required to be increased to a pressure of 30% to inhibit attack on 
Cereus petals. 
The magnitude of the exosmosis of nutrients may also be 
measured by noting the difference between the times necessary to 
produce infection when the spores are sown in nutrient and when 
the spores are sown in water, the spores in the former case being 
sown in a concentration sufficient to inhibit germination on glass 
in pure water. With increasing exosmosis the time difference 
becomes less and less, and in the case of certain petals (e.g. Cereus) 
may become infinitesimal. 
(3) On the physics of cuticular resistance and the penetrating power 
of fungi. 
Prom the fact that the fungal extract has no effect whatever 
when laid on cuticle, and from evidence obtained in the microscopi- 
