310 Dey. — Studies in the Physiology of Parasitism. V. 
The passage of the fungus through the cell-wall is associated with 
a swelling and dissolution of the cellulose layers. The first sign of this 
action on the wall is the disappearance of the uniform stratification of the 
cell-wall, and the appearance of a clearer area round the ‘ infection hypha ’. 
No such change in the subcuticular layers is to be noticed, however, before 
the break in the cuticle is effected. The cuticle apparently bars completely 
the passage into these layers of any enzyme secreted by the £ infection 
hypha’. The behaviour of C. Lindemuthianum is in this respect quite 
analogous with that of B. cinerea. 
The ‘ infection hypha after growing a short distance into the host, 
produces at its end a small vesicle (Figs. 9, 10, 11, 12, 13, 14) from which one 
or more branches emerge and spread through the host tissue. This vesicle 
may be developed in the swollen subcuticular layers of the wall, or its 
formation may be delayed till the ‘ infection hypha ’ has penetrated far into 
the cell. This vesicle appears to be similar to that described by Marshall 
Ward ( 13 ) for the infection process in Uredo dispersa ; the nature of this 
vesicle is obscure. 
The effect of the entrance of the hypha into the host-cell is to be 
observed in Figs. 14, 15, 16. From these figures it is evident that the 
collapse of the cell immediately beneath the place of entry takes place 
only after a hypha is well established in its cavity ; the invading hypha 
may be the original ‘infection hypha’ (Fig. 15) or a branch from the 
‘ vesicle ’ (Fig. 16). When the ‘ infection hypha 5 enters the cavity of the 
cell, the protoplasmic contents of the latter apparently flow towards the 
hypha and collect round it (Figs. 13, 14, 15). Movement of nuclei, similar 
to that found by Blackman and Welsford in the bean-cell invaded by 
B. cinerca , has never been observed in this case. 
The stomata of the host do not seem to afford an easier channel of 
infection than that through the epidermal cell. Only one instance of the 
passage of an ‘infection hypha’ through the stoma was found in all the material 
examined. Even there infection has taken place from an appressorium in 
the usual manner, and not directly by the germ-tube (Fig. 17). 
In conclusion, the author wishes to express his gratitude to Professor 
V. H. Blackman, at whose instigation the work was undertaken, and from 
whom he has throughout received most helpful criticism and advice. 
Summary. 
The spore of Colletotrichum Lindemuthianum , when germinating on 
the host plant, produces a germ-tube, which directly it comes in contact 
with the host surface develops at its end a thick- walled, dark-coloured 
appressorium. The appressorium becomes attached closely to the surface 
by the help of its mucilaginous envelope. 
