133 
‘ Biologic Forms ’ of the Erysiphaceae. 
the cells at the edge of the hole. By the seventh day flecks of mycelium, 
bearing young conidiophores, were produced round the margin of the hole. 
By the ninth day about a hundred mature conidiophores were visible, all 
close to the edge of the hole. On the fourteenth day small but vigorous 
mycelial patches, bearing conidiophores, were visible round the hole ; this 
part of the leaf was now yellow, translucent, and nearly dead. A few of 
the conidia which had been sown at a little distance from the hole produced 
a few short mycelial hyphae. 
In another experiment (No. 9) two uninjured wheat leaves, and one 
barley leaf in which a circular hole 4 mm. in diameter had been made with 
a cork-borer, were exposed for 48 hours to inoculation from ripe, bursting 
perithecia. On the seventh day (December 19) the two wheat leaves bore 
numerous minute flecks of mycelium ; the barley leaf bore small flecks of 
mycelial hyphae proceeding from germinating ascospores at the margin of 
the hole, at places where the epidermal cells had been dragged away in the 
process of stamping out the hole* On the tenth day each of the wheat leaves 
was covered, for the whole length (6 cm.) which had been exposed to the 
bursting perithecia, with very numerous, small, powdery Oidium- patches. 
No infection of the barley leaf had occurred except at the very edge of the 
hole, where at three places little patches of mycelium, bearing two to three 
conidiophores with chains of ripe conidia, were formed, and also several 
barren patches of mycelium. This leaf was decolourized, and on examina- 
tion was found to have been inoculated with ascospores all over its surface ; 
these spores had germinated everywhere, but except at the injured place 
had been unable to cause any infection. 
h . Injury caused by Slugs. 
Experiments were made in which barley leaves injured by the attacks 
of slugs were inoculated, conidia being used in the first two experiments, 
and ascospores in the last two. 
In the first experiment (8*) barley leaves were exposed for twelve 
hours to the attacks of some slugs kept in captivity, at the end of which 
time the leaves were much injured by having large pieces eaten out of them. 
The leaves were inoculated over their whole upper surface. After thirteen 
days infection was visible here and there along the edges of the bitten 
places, where vigorous little patches of mycelium bearing a few conidiophores 
were formed. By this time the leaf-cells in the neighbourhood of the 
injured places were yellowish, transparent, and nearly dead. It was notice- 
able that infection occurred most frequently at the places where the leaf had 
been bitten nearly to shreds. In another experiment (No. 12) one barley 
leaf, treated similarly to the above, bore on the sixth day several vigorous 
little patches of mycelium at the edge of the bitten places. These patches 
