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18 OUR SHADE TREES AND THEIR INSECT DEFOLIATORS. 
ing will accrue to the plant from the proportion of poison recommended. 
The new growth, that developed after the first poisoning, was protected 
by one-fourth of a pound to the barrel in 1882. From midsummer un- 
til autumn the unpoisoned half of the grove remainded denuded of 
foliage, while the poisoned half retained its verdure. The little damage 
then appearing in the protected part was mostly’done before the first 
treatment. Eggs were laid abundantly throughout the season. Many 
of these seemed unhealthy and failed to develop, probably because they 
were pvisoned. Many hatched, but the young larve soon died. The 
eggs were seldom deposited on the young leaves that were appearing 
after the poison was applied, but were attached to the developed leaves, 
and here the larve generally got the poison to prevent their attack 
upon the aftergrowth. Still the young leaves became perforated to 
some extent. The adults, which fly from tree to tree, appeared plenti 
fully without much interruption throughout the season, and often several 
could be seen feeding on each tree. Possibly many of these may have 
become poisoned before depositing the eggs. 
The efficiency of London purple being established, it will generally 
be preferred to other arsenicals, because of its cheapness, better diffus- 
ibility, visibility on the foliage, &c. As the effects of the poisons com- 
monly do not appear decidedly for two or three days after their admin- 
istration, the importance of the preventive method of poisoning in 
advance cannot be too strongly urged. As the effect is slow in appear- 
ing, impatient parties will be apt to repoison on the second or third day, 
and thus put on enough to hurt the plant when the effect does come. 
Much depends on dryness or wetness of the weather; but good effects 
may be expected by the third or fourth day. 
London purple seems to injure the plant less than Paris green. 
Treatment with Paris greea.—In 1883 the Paris green was first applied 
on the 29th of May, at which date the eggs were extremely abundant 
and hatching rapidly on the leaves. Paris green, flour, and water were 
mixed by the means previously employed with London purple and 
already described. The mixture was applied to the north part of the 
same grove of elms. Thus far experience shows that the Paris green 
is effective against the insect, but that this poison injures the plant more 
than does the London purple. 
Three-fourths of a pound of Paris green to a barrel (36 or 40 gallons) 
of water, with 3 quarts of flour, may be regarded as a poison mixture 
of medium or average strength for treating elms against these beetles, 
and the indications thus far are that the amount of Paris green should 
not be increased above one pound or be diminished much below oune- 
half a pound in this mixture. To a bucketful of water three-fourths of 
an ounce of Paris green may be used. The action of this poison is 
slow but severe, and varies much with the weather. Thus far the re 
sults of tests have been varied so much by the weather and different 
modes of preparation and application that they will be repeated. When 
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