Studies in the Physiology of Parasitism . 1 
III. On the Relation between the ‘Infection Drop 5 and the 
underlying Host Tissue. 
BY 
WILLIAM BROWN, M.A., D.Sc., 
From the Department of Plant Physiology and Pathology , Imperial College of Science and 
Technology , London. 
I N the first of these studies, when the general action of the extract of 
Botrytis cinerea was examined, it was found that the cuticle appeared 
to offer a great obstacle to the action of the extract, so that in order to 
obtain rapid results it was necessary to inject the extract into the tissues. 
The object of the present paper is to examine the relation of the extract to 
cuticle, and more generally to determine the relation of the 4 infection drop ’ 2 
to the underlying tissue of the host plant. This problem is of considerable 
biological interest, as on its solution will depend to a large extent our con- 
ception of the physiology of the early stages of parasitic attack by fungi of 
the type of Botrytis. 
The only work which deals directly with this question is that of 
de Rary and of Nordhausen. De Bary 3 examined the early stages of the 
attack by Sclerotinia Libertiana on the stems of broad bean. Placing 
the bean stems a short distance in front of the advancing hyphae, he 
was able to arrange that the latter came in contact with the surface of 
the stem after a short passage through the air ; the stem was thus in con- 
tact with the aerial portion only of the mycelium. Under these circum- 
stances, the hyphae did not immediately enter the tissue but proceeded to 
form attachment organs. While these were being formed de Bary noted 
that the underlying cells collapsed and became blackened ; and this at 
a time when, as he states, the fungus had not yet penetrated the cuticle 
of the plant. As a consequence of the death of the underlying cells an 
exosmosis of nutrient material took place on to the surface. The fungus, 
1 For No. I of this series see Ann. Bot., vol. xxix, 1915, p. 313 ; for No. II, see Ann. Bot., 
vol. xxx, 1916, p. 389. 
2 By this term is meant the drop of fluid in which the spores lie upon the surface of the plant. 
3 de Bary, A. . Ueber einige Sclerotinien und Sclerotienkrankheiten. Bot. Zeit., 1886. 
[Annals of Botany, Vol. XXX. No. CXIX. July, 1916.] 
