Studies in the Physiology of Parasitism. 
V. Infection by Colletotrichum Linde muthianum. 
BY 
P. K. DEY, B.Sc. 
From the Department of Plant Physiology and Pathology , Imperial College of Science and 
Technology, London. 
With Plate XXI. 
I N all previous works on bean anthracnose caused by the well-known 
parasite Colletotrichum Lindeniuthianum , no observations of the actual 
mode of infection have been made. Whetzel (14) gives a diagram of 
penetration of the germ-tube through the outer surface of the bean-pod but 
he does not appear to have made any study of the details of penetration. 
Frank (6) observed that the germ-tubes of C. Lindeniuthianum produced on 
the surface of the host dark-brown appressoria from which infection took 
place, but he neither described nor gave any figures of the process of 
infection. 
In the case of infection by Botrytis cinerea , workers like Biisgen (4) 
and Marshall Ward (12), believed that the germ-tube effected its entrance by 
softening and dissolving the cuticularized epidermal wall of the host ; 
Voges (11) also speaks of the slime formed by the germ-tube of Fusicladium 
softening the cuticle. But, as pointed out by Blackman and Welsford (1), 
no critical observations were in any case made. It was Brown (2) who, 
working with B. cinerea , first showed that the cuticle of the host is quite 
unaffected by the powerful extract which he obtained from young hyphae. 
When such an extract is placed on a delicate, uninjured rose petal, the 
cuticle and the underlying tissue remain unchanged ; when placed on 
wounded petals, however, disorganization of the tissue takes place in a very 
short time. He thus indicated that the germ-tubes of B. cinerea have no 
power of causing a softening of the cuticle, and that the latter is im- 
permeable to the enzymes which dissolve the non-cuticularized walls. It 
thus seemed probable that penetration of the cuticle by the germ-tube takes 
place by mechanical means. Blackman and Welsford (1) made careful 
microscopic study of this question, and showed that the passage of the germ- 
[ Annals of Botany, Vol. XXXIII. No. CXXXI. July, igig.] 
