1921] MILES—LEAF SPOTS OF ELM 165 
SYMPTOMS 
The disease makes its appearance early in the spring, the 
amount of primary infection apparently being dependent to a con- 
siderable degree on the weather conditions, as it is much worse on 
the same tree in some years than in others. CLINTON expressed 
the opinion that the only infection which occurred was the primary 
spring infection, and that there was no further spread during the 
summer. The fact that no conidial or summer stage had ever 
been found connected with the disease, and also his observation of 
trees which shed all their leaves early in the season and which 
later produced a new crop of foliage entirely free from spots, would 
tend to support this conclusion. The absence of the disease on 
the new crop of leaves, however, might have been due to weather 
conditions which were not favorable to the spread of the organism 
at that time. In any case, the writer has found a conidial stage 
constantly associated with the disease in every specimen examined, 
and the connection between the two stages will be clearly shown 
later. Observations show also that the primary infection is con- 
fined almost exclusively to the lowest leaves, and that it is much 
more abundant on the young seedlings, whose leaves are naturally 
closer to the ground, and to the ascospores which are the source of 
this early infection. Moreover, it is only on these young seedlings 
that twig and petiole infection has been observed, although there it 
is often quite severe, killing off the entire new growth. 
The first evidence of the disease is a small whitish or yellowish 
fleck or blotch on the upper side of the leaf shortly after it has 
unfolded. This spot increases in size, and soon a number of small 
black specks begin to appear within the whitened area. As 
these enlarge they sometimes coalesce to form a single, coal black, 
stroma-like, subcuticular structure which is quite irregular in out- 
line and varies from 0.5 to 2 or 3mm. in diameter. As a rule, 
however, the individual stromata remain separate, when they 
appear to be somewhat concentrically arranged, forming a distinct 
spot, in most cases surrounded by a narrow band of whitish dead 
tissue as shown in fig. 12. Occasionally the black stroma, or the 
group of separate stromata, so closely grouped together as to seem 
to the naked eye to be a single one, may cover the entire discolored 
