1 1 2 Brown. — Studies in the Physiology of Parasitism. VIII. 
experiments with Rose petals, where it was found that infection could be 
produced even when the spores were put on so thickly as to constitute 
a paste. Thus, while in the germination tests on glass it is readily possible 
to inhibit germination by increasing the concentration of spore sowing, the 
same is not possible in sowings on the petal itself. 
On examining the dense suspension of spores which had begun to give 
infection of the petal it was seen that only a few spores had germinated, 
and these in the neighbourhood of the spots where attack was beginning. 
The apparent discrepancy is therefore probably explicable on the ground 
that in the case of the germination tests on glass the small quantity of 
nutrient is divided between a very large number of spores and produces no 
apparent effect as regards germination, whereas in the case of the infection 
drops on the petal itself the nutrient reaches the drop unilaterally, and 
probably therefore is completely taken up by the spores lying in contact 
with the plant surface. The latter would thus be able to germinate and 
produce infection while the great bulk of the spores present remain 
ungerminated and ineffective. 
Exosmosis from Foliage Leaves. 
The examination of foliage leaves in the present connexion has not 
been carried out in the same detail as in the case of floral structures. The 
reason for this lies in the fact that difficulty was experienced in obtaining 
a suitable plant and a suitable fungus for investigation. 
All the petals examined show the common feature that they are readily 
attacked by spores of Botrytis when the latter are placed on the petal in 
suspension in pure water. In such a case therefore it is possible to examine 
the phenomenon of exosmosis in relation to attack. Up to the present, 
however, no plant has come under observation the leaves of which can be 
parasitized by Botrytis in this manner. Even with the leaves of Broad 
Bean, which have been so much used in investigations of parasitism of the 
Botrytis type, no satisfactory infection is shown when the fungal spores are 
placed on the leaf in pure water, though it takes place readily when 
extraneous nutrient is supplied. In these circumstances one has to be 
contented with examining the negative side of the problem, i. e. the relation 
between the particular exosmosis features presenting themselves and the 
absence of attack. 
Measurements have been made of the exosmosis from leaves of Broad 
Bean, French Bean, and Tradescantia discolor. In all these cases very 
complete wetting of the leaves took place and high figures were obtained 
in the conductivity determinations. Thus in one experiment where a 
comparison was made between Beans grown in the open at ordinary 
temperature and others forced in a greenhouse at a higher temperature, 
the following figures for conductivity were obtained. (The leaves were all 
