
Endophytic Adaptation shown by Erysiphe Graminis DC. 367 
the conidia were sown on the sub-epidermal or deeper layers of the exposed 
mesophyll, or even on the internal surface of the lower epidermis. After 
inoculation, the leaves were placed on damp blotting-paper in a Petri dish. 
By the sixth to eighth day vigorous infection had nearly always resulted, 
the surface of the wound bearing patches of clustered conidiophores. The 
leaves were then fixed in Flemming’s fluid or in chromacetic, and subse- 
quently embedded in paraffin, microtomed, and stained with Diamant fuchsin 
and Lichteriin. ; 
It was found on examining such wcunded leaves that the fungus had 
invaded the internal tissues to a remarkable extent. Where the mesophyll- 
cells remaining uninjured were several layers deep, the byphe had penetrated 
inwards, winding through the intercellular spaces as far as the internal 
surface of the lower epidermis. Haustoria were sent into the cells of the 
superficial layer of the mesophyll by the hyphe creeping on the surface of the 
wound, and into all the deeper layers of the mesophyll by the hyphe running 
in the intercellular spaces. The cells of the lower epidermis were also 
attacked, the internal wall having been penetrated. The sheath-cells of the 
vascular bundles were much invaded by very vigorous haustoria. The 
haustoria formed in the cells of the internal tissues resemble in every way 
those which occur normally in the epidermal cells. 
The hyphe enclosed in intercellular spaces, either just below the surface of 
the wound or deep down in the internal tissues, struggle to produce conidio- 
phores. The respiratory cavities over the stomata of the lower epidermis 
were in a great number of cases full of vigorous hyphe producing young 
conidiophores. When the intercellular space, where the young conidiophore 
was produced, was shut off from the open air by only a thin membrane con- 
sisting of the walls of collapsed mesophyll-cells, the young conidiophore 
erowing upwards, sometimes proved able to break through it and continue its 
growth. The direction of growth of the young conidiophores produced in the 
respiratory cavities and other intercellular spaces was usually vertical, and 
towards the surface of the wound. Examples were observed, however, of 
young conidiophores growing horizontally in intercellular spaces between the 
mesophyll-cells, or, in a few cases, vertically, with the apex of the conidio- 
phore directed away from the surface of the wound. 
In several cases hyphz had penetrated laterally, in a direction parallel to 
the surface of the leaf, from the edge of the wound, and occurred in the 
intercellular spaces in the middle of the mesophyll, at places where all the 
tissues, including the epidermis above and below, were uninjured. In such 
places both haustcria and young conidiophores were produced. 
Figures are given illustrating the details of the growth of the hyphe in 
