1921] MILES—LEAF SPOTS OF ELM 177 
water to serve as checks. Each set was kept under a bell jar, 
whose inner surface had been lined with moist filter paper, for a 
period of 42 hours, after which they were left in the normal atmos- 
phere of the greenhouse. A like number of twigs of U. americana, 
whose leaves had unfolded normally outside the greenhouse, were 
treated in a similar manner. As was to be expected from the 
failure to secure germination of the ascospores on the leaves of the 
English elm, no infection occurred on that host. On April 25, 
however, or after a period of about three weeks, eight leaves of the 
American elm were found to bear well defined spots quite charac- 
teristic of the early stages of Gnomonia ulmea. Two of these 
leaves bore three spots each, another one two, and the other six 
had only a single one on each. These spots showed well developed 
pustules of the conidial stage, which is to be described later. In 
addition to these well defined spots a number of leaves showed 
small whitish flecks or blotches, thereby indicating that if the 
experiment had been allowed to continue for a longer period the 
percentage of infection would have been higher. 
OBSERVATIONS ON OVER-WINTERING 
A number of observations have been made on the over-wintering 
of the fungus on elm leaves under various conditions, and some 
attempts have been made to hasten its development by placing 
the leaves under various controlled conditions. Leaves on which 
the spots occurred were brought into the laboratory, both before 
and after they had been severely frosted, and some were immersed 
in water, both at room temperature and in the refrigerator. Others 
were placed in a moist chamber suspended over water, both in the 
laboratory and refrigerator, and others were placed in each of 
these places under their normal conditions of humidity. Still 
others were suspended over calcium chloride in each of these 
temperatures in order to assure a dry atmosphere. It was found 
that no further development occurred in the leaves which were 
immersed in water, and that the fungus soon died, the perithecia 
becoming mere empty husks. This was confirmed by comparison 
with leaves which had wintered normally outside the laboratory. 
On leaves which had been buried slightly in the soil or were in close 
