176 BOTANICAL GAZETTE [MARCH 
This led to a further attempt to germinate the spores on the leaves 
of both the English and the Scotch elm, U. glabra, but without 
success in either case. A considerable percentage of germination, 
however, was always obtained with U. americana. These experi- 
ments would seem to indicate that the germination of the asco- 
spores of Gnomonia ulmea is dependent on a special stimulus of 
some sort exerted by the leaves of susceptible species of Ulmus, but 
which is absent in the leaves of other species of the same genus, 
just as it is absent in tap or distilled water, and the various liquid 
and solid nutrient media in which attempts were made to grow 
the fungus. 
At the end of twelve hours of contact with the leaf of the 
American elm under suitable moisture conditions, as previously 
stated, the spores were found in various stages of germination. 
Wherever two spores lay in contact with each other and also wi 
the leaf, there was noted a brown coloring matter deposited between 
them. This coloring matter is similar to that previously mentioned 
as being deposited between the hyphae of the stroma andon thelower 
side of the cuticle. The germ tube usually arises from the large 
cell of the spore only, as shown by fig. 20, although in a very few 
instances the small cell also may send out one. Germination 
apparently can occur from any point in the spore, although usually 
the germ tube makes its exit from the side of the large cell. One 
can tell where the germ tube is going to form even before any 
swelling occurs by the excretion of the brown coloring matter on 
the outside of the spore wall at that point. As the tube grows, 
the coloring substance is deposited along its entire length, except 
at the extreme apex, but in considerably greater density at the 
point where it leaves the spore. The substance is present in 
greater abundance also wherever two germ tubes touch or cross 
each other. 
INOCULATION WITH ASCOSPORES 
On April 6 a number of abscissed twigs of Ulmus campestris, 
whose leaves had unfolded in the greenhouse, were inoculated 
with the ascopores of Gnomonia ulmea. Twelve twigs were used, 
six being sprayed by means of an atomizer with a suspension of 
spores, while six similar ones were sprayed with sterile distilled 
