130 Salmon — Further Cultural Experiments with 
Part II . — In the Experiments described below, the Fungus used in 
inoculation was the i biologic form ’ of Erysiphe Graminis DC. on wheat. 
a. Injury by ‘cuts 1 .’ 
In four experiments (Exper. Nos. a 17, a 22, a 46, a 065) conidia were 
sown on thirty-one ‘ cut ’ barley leaves 2 , on the cells of the mesophyll 
tissue exposed by the cut. Infection resulted on sixteen of these leaves, 
minute patches of mycelium bearing numerous conidiophores appearing in 
nine to fourteen days. 
In one experiment (No. a 45) a sharp razor was drawn longitudinally 
along the blade of the leaf, making a fine slit-like cut, which extended to, 
but did not cut through, the lower epidermis. A cut of this nature, 1*5 cm. 
to 2 cm. long, was made on five leaves. In the case of four leaves infection 
resulted along the edge of the cut, where numerous patches of mycelium 
were produced, and on three leaves a few scattered conidiophores were 
produced by a few of the patches of mycelium bordering the cut. 
Uninjured barley leaves were then inoculated with ascospores. In 
the first experiment (No. j) two wheat leaves and two barley leaves, both 
attached to seedling plants in pots, were introduced into a Petri dish, at 
the bottom of which wheat leaves bearing ripe and bursting perithecia were 
placed. The four leaves were fixed horizontally at a little distance above 
the perithecia, and exposed for three days to inoculation by the ascospores 
which were being continuously thrown up. At the end of this time the two 
pots of wheat and barley with the four inoculated and marked leaves were 
placed under a bell-jar. On the fifth day (November 28) the two wheat 
leaves bore very numerous (fifty to eighty) minute flecks of mycelium. No 
trace of infection appeared on the barley. On the seventh day many of the 
patches on the wheat leaves bore groups of ripe conidiophores ; the nine 
control leaves were all free. On the tenth day the two wheat leaves were 
covered almost continuously on the upper surface for two-thirds of their 
length with densely powdery Oidium- patches ; the controls were still all 
free. No signs of any infection appeared on the barley 3 . 
In the next experiment (No. 2) leaves of wheat and barley were removed 
from plants and inoculated with ascospores, with the object of seeing if the 
injury to the barley leaf caused by its removal from the plant would bring 
about susceptibility. Two wheat leaves and two barley leaves were exposed 
for three days to ripe, bursting perithecia. On the tenth day the two 
1 The manner in which the cut was made has been described in (1), p. 108. 
2 In all the experiments the first leaf of seedling plants was used. 
8 A dozen pots of seedling plants of barley were allowed to stand for four months in a green- 
house, among pots of wheat plants virulently infected with Oidium , and were constantly inoculated 
by conidia blowing on to the leaves and stems. No trace of any infection appeared on the barley, 
notwithstanding that the health of the plants became much impaired by unfavourable conditions 
©f growth. 
