B74 . [ AssEMBLY 
the first season of its appearance, for it is doubtful if it could ever 
become so harmful without accumulating strength by the growth of 
previous years. 
The disease is readily recognized. By the latter part of May the 
leaves of an affected tree show very considerable contortion or 
crumpling, which continues to increase until the leaves have quite 
lost their normal appearance and grown into baggy folds and 
wrinkles, and at the same time become somewhat thickened. ‘The 
whole leaf is not always affected; often a greatly-distorted leaf will 
have —it may be the apex—dquite unaffected and normal. In 
about a month the surface of the leaf takes on a whitishness or 
bloom, especially upon the under side, and the leaves soon drop 
from the tree. In severe attacks the tree is almost or quite defoli- 
ated, the branches becoming about as bare as in early spring. More 
usually, however, new leaves are developed as fast as the diseased 
ones fall, so that while the ground is strewn with cast-off leaves the 
tree continues in full foliage. In either case, by the latter part of 
July the trees will be well provided with a second crop of healthy 
leaves. 
The parasitic fungus which causes the disease grows exclusively 
inside the tissues of the tree. Although the mycelium is abundant 
it is dificult to detect on account of its delicacy and transparency. 
It was first seen in the leaf by Prillieux* in 1872, and Frankt has 
since detected it extending from the leaves through the veins and 
leaf-stalks into the bast bundles of the smaller branches. It insinu- 
ates itself between the cuticle and cells of the lower surface of the 
leaf, and there produces in June its numerous spores in minute sacs, 
each containing from six to eight. It is this fruiting of the fungus 
that gives the whitish bloom to the leaf just before it falls. 
Nothing whatever is known of the way in which the spores trans- 
mit the disease, and it is difficult to frame plausible conjectures. 
The mycelium is, however, perennial, and lives from year to year in 
the younger branches, running out through the leaf-stalks and occu- 
pying the new leaves each season. One may easily convince him- 
self of the probability of this by carefully watching a tree known to 
be infested, for he will be able to detect more or less evident traces 
of the disease from the earliest appearance of the leaves in spring 
to their fall in autumn; and having become familiar with these signs 
will be able to tell it in trees whose condition is not previously 
known to him. ; 
The curl pays no regard to the condition of a tree, but may be 
found in the thriftiest, as well as in the weakest. Its life, however, 
is so thoroughly bound up with the life of its host that whatever 
influences the health of the tree, influences the health of the fungus, 
although not always to just the same degree. The harmfulness 
arises from two sources, first the necessity of the tree providing not - 
only for its own nourishment but also for that of a voracious para- 
* Bull. Soc. Botanique de France, 1872, p. 227. 
+ Krankheiten der Pflanze#, p. 526. 

