1921] MILES—LEAF SPOTS OF ELM 175 
extract of dried elm leaves, and sugar solutions, to solid media 
such as the agars of cornmeal, bean, potato, Brazil nut, onion, 
elm leaf, and plain washed agar. In distilled or tap water the 
spores swelled considerably, especially the larger cell, and some- 
times a spore would give the appearance of being on the point of 
sending out a germ tube from the side of the larger cell, but this 
never occurred. This is in accordance with the results obtained 
by KLEBAHN (27) in Guomonia alniella and Gnomoniella tubiformis, 
which he was not able to grow in culture, but is contrary to his 
results with Gnomonia platani and G. leptostyla, both of which 
grew well on nutrient media, the latter even producing the peri- 
thecial stage in such cultures. It would seem that the ascospores 
of Gnomonia ulmea, as in G. alniella and Gnomoniella tubiformis, 
require the stimulation given by the green leaf of the host plant 
itself in order to induce germination. WoLF (42) found that this 
was the case in Diplocarpon rosae, the ascospores of which would 
not even germinate in a drop of water in which a portion of a 
green leaf of the host had been placed, but must be placed in a 
drop of water directly on the living leaf itself. This assumption 
was later confirmed by experimentation. Toward the middle of 
March a number of twigs were cut from an elm and placed in the 
greenhouse with their cut ends immersed in water. In about 
three weeks the buds on these twigs unfolded. A number of the 
young leaves were removed and placed in a moist chamber with 
their surfaces in contact with a slide on which a large number of 
the expelled spores of Gnomonia ulmea had been intercepted as 
previously described. Intimate contact was secured by moistening 
the surface of the slide to which the spores adhered with a drop 
of water. By removing the leaf it was possible to examine the 
spores on the slide by means of a microscope, but never was one 
of them found to have germinated. Later, when the leaves on the 
trees outside the greenhouse had begun to unfold, the same experi- 
ment was attempted again, and in twelve hours it was found that 
a considerable number of the spores in contact with the leaves 
had germinated. This led to an examination of the tree from 
which the leaves used in the first experiment had been obtained, 
and it was ascertained to be an English elm, Ulmus campestris. 
