‘ Biologic Forms' of the Erysiphaceae. 13 1 
wheat leaves were covered, over the inoculated surface, with little powdery 
Oidium- patches, about thirty on each leaf. No signs of any infection were 
visible on the barley, although the surface of both leaves was covered with 
many hundreds of germinating ascospores which had been ejected from the 
perithecia. The number of the ascospores was so great that here and there, 
at places where hundreds had germinated together, a whitish-looking patch 
had been produced. There was not the slightest sign of any infection, 
however. 
Experiments were then made to see whether ascospores would be able 
to infect ‘ cut * leaves of barley. 
In the first experiment (No. 3) three barley leaves were removed from 
the plant and ‘ cut ’ on the upper surface ; they were then suspended over 
ripe perithecia for 48 hours with the ‘ cut * surface upwards. On the fourth 
day several germinating ascospores were visible opposite the ‘ cut ’ on one 
leaf, and formation of a lobed haustorium from several of the appressoria 
had taken place. On the fifth day three vigorously growing patches 
of mycelial hyphae proceeding from germinating ascospores were visible 
on this one barley leaf, on the epidermal cells opposite the ‘ cut.’ 
On the seventh day a few young conidiophores were produced, and on the 
ninth day ripe conidiophores. On the tenth day all the leaves were yellow 
and translucent. No infection was visible on two leaves; on the third 
leaf three patches of mycelium, each bearing conidiophores, were visible 
opposite the 4 cut 5 ; also two small patches of mycelium, each proceeding 
from a single ascospore and each bearing two or three conidiophores, were 
visible at a distance of 1 mm. beyond the region opposite the ‘cut.’ 
On the remaining parts of this same leaf could be seen hundreds of 
ascospores which had been ejected from the perithecia, and which had 
germinated, but, being on cells out of reach of the influence caused by the 
injury, had failed to produce any infection. 
In the second experiment (No. 4) four 4 cut ’ barley leaves were inoculated 
with drops of water containing ascospores (obtained by crushing ripe 
perithecia in the water). The drop was placed on the uninjured epidermis 
opposite the * cut 5 in the case of two leaves, and 011 the cut surface of the 
other two leaves. On the eighth day a vigorous patch of mycelium with 
a few young conidiophores was visible on the cut surface (i.e. on cells 
of the exposed mesophyll) of one leaf. On the twelfth day this leaf 
bore a vigorous radiating mycelial patch with several conidiophores. 
In the remaining two experiments (Nos. 5, 7) six barley leaves were 
removed from plants and 4 cut/ and were then exposed for 48 hours to 
inoculation from ripe, bursting perithecia. Two leaves were exposed with 
the 4 cut ’ surface downwards (I. e. facing the perithecia), and four with the 
‘ cut 5 surface upwards. At the end of the forty-eight hours germinating 
ascospores, with appressoria formed, were visible on all the leaves at the 
K % 
