12 THE IMPORTED ELM LEAF-BEETLE. 
west side only half consumed and comparatively green. Such are aver- 
age cases. 
The inferences have been that the shade, dampness, and coolness of 
the tree on the northwest side during the morning is too unhealthy for 
the favorable development of the larvae or of the eggs deposited there ; 
but whether this be true or not, the insect probably prefers to deposit 
chiefly in the middle of the forenoon, and on that part of the tree which 
is then warmest. This would give a greater number of the eggs at the 
outset on the southeast side, as observation seems to confirm, and since 
the young larvae do not migrate to any noteworthy extent, the one-sided - 
ness described would result whether the northwest side were unhealthy 
or not. The former explanation is most probably the correct one, as we 
have noticed that the insect is less injurious during very wet summers. 
Preferences of the Elm Beetles for certain Varieties and Species of Elms. — 
The American Slippery Kim does not occur in this grove, but only one 
native species, the common American Elm, Ulmus americana. This is 
practically free from the ravages of the beetle, on which account it may 
be preferred to the European species. It is tall, and has gracefully 
arched branches, making it as ornamental as any European kind, yet 
as a shade tree it does not equal the U. montana of the Old World. The 
latter has a broader, denser crown, but the attack on it is considerable, 
enough to leave the choice in favor of the American species. 
U. montana seems the best European species grown here for shade, 
since the other foreign elms here cultivated are not dense enough. This 
applies to U. campestris, V. suberosa, V. effusa, and U. parvifolia (siber- 
ica >. The last named is not attacked as much as the American. The 
young larvae cannot develop on it, but die quite soon, without growing, 
and they gnaw the leaves very little. The other foreign species men- 
tioned are seriously eaten; the severest attack being upon the U. cam- 
pestris, the favorite food of this insect. 
As early as June 25, in 1883, this species was completely eaten and 
biown in our grove, at which date the U. montana examples retained 
more than half their verdure — in some individuals nearly all — and the 
common American elm was perfectly green. The U. campestris is one of 
the poorest elms for shade, and its total abolishment throughout the 
entire country would probably lessen the assault on TJ. montana to a 
comparatively unobjectionable extent. This measure should be insti- 
tuted against the pest, and for the sake of the other species of elms. 
Effects of arsenical Poisons on Insect and Plant. — Species of elms are 
somewhat differently affected by the poison. When treated alike there 
is always manifest some difference in the susceptibility of different elms 
to the corrosive effects of the poison. Even individuals .of the same 
species or variety are differently impaired. As a rule, those which suit 
the insect best are injured most by the poison, and those which resist 
the insect most withstand the poison best. The latter have coarser 
foliage, with darker green color and more vigorous general growth; the 
