MANORANJAN MITRA 69 
7. RELATION OF PARASITE TO HOST. 
The examination of inoculated leaves shows that infection can take place 
either through a stoma or through any epidermal cell on either side of the leaf. 
(a) Infection through a stoma. The hypha near a stoma gives out a narrow 
tube which after passing through it again swells up and resumes its usual size. 
It spreads a little in the sub-stomatal space and then passes on to other cells 
(Plate IV, fig. 1). 
(b) Infection by piercing the epidermis. The infection can take place from 
any cell of the epidermis but is more common from the thin-walled motor cells 
(Plate LV, figs. 2—4). The hypha either directly penetrates the epidermis or 
under the cuticle parallel to the outer wall of the epidermis to some extent, and 
then goes down either into an epidermal cell or between the side walls of two 
cells to ceils deeper in. Sometimes when it is passing between the side walls of 
two cells, it sends a branch into one of them. Sometimes after inoculation the 
hyphe are found in large amount under the cuticle but none in the cells below. 
Generally, before entering, the hypha coming in contact with the cuticle swells 
up and gives out a narrow tube which after penetrating the epidermis again 
swells up. Frequently the hypha presses down the cuticle of an epidermal cell 
to effect an entrance. After entering it may branch and fill the epidermal cell 
with a mass of mycelium or may directly penetrate deeply into the tissue of the 
leaf by passing from cell to cell and ramifying both in the thin-walled parenchy- 
matous and the sclerenchymatous cells, and later may enter the vascular 
bundles. 
- It is both intra and inter-cellular. Haustoria are not found. In passing 
from cell to cell the hypha gives out a narrow tube which pierces the wall and on 
entering the opposite cell again resumes its former thickness. The fungus can 
invade new areas by passing along the vessels of the xylem (Plate IV, fig. 6). It 
cannot penetrate the midrib directly, but generally infection takes place from 
hyphe passing in through the motor cells just on either side of it. The intra- 
and inter-cellular hyphe are very clearly seen in the midrib region, and here 
sometimes they spread more through the inter-cellular spaces which are found 
at the angles of two or more cells (Pl. IV, fig. 5) than through the cells. Fre- 
quently the fungus forms stromatic masses in the epidermal cells on both sides 
of the leaf, sometimes in quantity sufficient to rupture the cuticle. In 
sclerenchymatous cells and in the vascular bundles hyphe often swell up to 
such an extent so as to fill the cavity. 
The fungus kills the cells in advance of its growth, and penetration of the 
dead cells is evidently easier than of the living, since in the central dead portion 
