Studies in the Physiology of Parasitism. 
VIII. On the Exosmosis of Nutrient Substances from the 
Host Tissue into the Infection Drop. 
BY 
WILLIAM BROWN, M.A., D.Sc. 
(. From the Department of Plant Physiology and Pathology , Imperial College of Science and 
Technology , London.) 
With one Figure in the Text. 
I N previous papers of this series 1 it was shown that the fungus Botrytis 
cinerea , though possessing an active cytolytic principle, was unable to 
act upon the cells of the host tissue so long as an intact cuticle separated 
it from them. Evidence was brought forward to show that the penetration 
of the cuticular membrane was effected by mechanical rupture, and it was 
only when this had taken place that the fungus was able to attack 
directly the host cells. So far the question had been treated from the 
point of view of the influence of the parasite upon the host. There still 
remained for examination the converse relation of host to parasite. For 
whereas, antecedent to penetration, the tissue of the host was found to 
be wholly unaffected by the presence of the parasite, it appeared not 
improbable that the host plant might be able to influence in some way the 
behaviour of the parasite. Such an influence might take the form of 
a stimulus to germination or of a chemotropic stimulus. The present paper 
deals with the former question, viz. with the passive exosmosis of nutrient 
material from the host cells through the cuticle. 
The method of experiment generally was as follows : Drops of distilled 
water of a standard size (c. 0-05 c.c.) were laid on the surface of plant organs 
and allowed to remain for some time, generally for twenty-four hours. 
They were then removed and examined to see whether any change had 
taken place in them due to their having been in contact with the plant. 
Two methods of examination were adopted : 
(1) Determination of the electrical conductivity of the fluid. 
(2) Determination of the effect of the fluid on the germination of fungal 
spores. 
1 Ann. Bot., vol. xxx, 1916, pp. 389, 399. 
[Annals of Botany, Vol. XXXVI. No. CXLI. January, 1922.] 
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