Studies in the Physiology of Parasitism . 1 
II. Infection by Botrytis cinerea. 
BY 
V. H. BLACKMAN, Sc.D., F.R.S., 
AND 
E. J. WELSFORD, F.L.S., 
From Ike Department of Plant Physiology and Pathology , Imperial College of Science 
and Technology , London. 
With Plate X and two Figures in the Text. 
T HE germ tubes of parasitic fungi which are not wound parasites 
usually infect the aerial parts of plants by entering through the 
stomata or by boring through the outer walls of the epidermal cells. In 
the case of stomatal infection the epidermal defences of the host plant are 
completely turned and infection is a comparatively easy matter, since many 
fungi possess enzymes which are able to cause disorganization of the 
cellulose walls of parenchyma cells. 
Where, however, the cuticle is perforated, our knowledge of the 
mechanism employed by the germ tube is very meagre. Busgen (3) has 
pointed out the importance of appressorta in many cases in bringing the 
fungus in close contact with the host. Most authors assume, as apparently 
does Busgen, that the germ tube softens and dissolves the cuticularized 
epidermal wall in the same way as a cellulose wall. For example, Marshall 
Ward (11), in his classical paper on a disease of the Lily due to Botrytis , 
speaks of the germ tube as dissolving its way through the cuticle. 
Miyoshi (5, p. 286 ) is of opinion that the perforation of many membranes 
of fungi is due to the secretion of enzymes, although he had been able to 
show that Botrytis cinerea could perforate a membrane such as gold leaf, 
upon which it could by no possibility act chemically. Voges (10) speaks 
of the slime formed by the germ tube of Fusicladium softening the cuticle. 
Such a view, however, has never been supported by physiological evidence 
1 The first of this series of studies appeared in the Annals of Botany, vol. xxix, 1915, p. 313. 
[Annals of Botany, Vol. XXX. No. CXIX. July, 1916 . 1 
