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REPORT OF THE ENTOMOLOGIST. 537 



tion on Plate V. In this caRO a tank mado especially for the purpose 

 is luounted in the high was^fHi-hox and secured by cleats, and sup- 

 ports a small hoso-roel. The so-called "San Jose nozzle" (a direct 

 discharge nozzle) is used. A feature of tlie illustration is the long 

 portable ladder, which can be handled by one man. Such an appa 

 ratus as this would be well adapted for use against the Web-worm. 

 It could be readily constructed and kept for years by the parking- 

 authorities of any city liable to the attacks of this or other leaf -eat- 

 ing shade-tree pests. 



In the use of arsenical poisons a number of points were brought 

 out by the series of experiments upon the Elm Leaf -beetle which are 

 imi;)ortant, and which may be briefly adverted to here: 



Certain trees are more susceptible to the corrosive effects of the 

 arsenic tlian others. The 1883 experiments were confined to Elms, 

 and we have no reliable data as to the relative susceptibility of other 

 shade trees; so that we can simply mention the ^jrobability that those 

 trees which are most liked by worms are more apt to be affected by 

 the poison than trees which are distasteful to the worms. 



"After each rain the poison takes a new effect upon the plant and 

 the pest, which indicates that the poison is absorbed more or is more 

 active when wot, and that it acts by dehydrating thereafter. Where 

 the tree is too strongly poisoned each rain causes a new lot of leaves 

 to become discolored by the poison or to fall. On some of the trees 

 the discoloration appears in brown dead blotches on the foliage, 

 chiefly about the gnawed places and margins, while in other instances 

 many of the leaves turn yellow, and others fall without change of 

 color, * * * 



"The poison not only produces the local effects from contact with 

 the parts touched by it, but following this there appears a more gen- 

 eral effect, manifested in that all the foliage appears to lose, to some 

 extent, its freshness and vitality. This secondary influence is proba- 

 bly from poisoning of the sap in a moderate degree. When this is 

 once observable no leaf -eater thrives upon the foliage. Slight over- 

 poisoning seems to have a tonic or invigorating effect on the trees." 



Inthe case of the Elm Leaf -beetle it was found that a preventive 

 apijlication of the poison was valuable. It was made while the eggs 

 were being deposited and before the young larvae were hatched, in 

 order to prevent the worms from getting a -start. It had the addi- 

 tional advantage of injuring the tree less than when applied later in 

 the season, as the caustic effect of the poison is greater when it comes 

 in contact with the sap at the gnawed edges and surfaces of the 

 leaves. 



It wag found advisable in 1883 to mix a certain amount of flour 

 with the Paris green or London purple used, in order to render the 

 mixture adhesive to the leaves. Three quarts of flour were used to 

 the barrel (40 gallons) of water. Where London purple was used it 

 was noted that the minimum amount per barrel of water was one- 

 fourth of a pound and the maximum three-fourths of a pound. Less 

 •than the minimum did not kill the larvee and more than the maxi- 

 mum injured the foliage. Three-eighths of a pound was recom- 

 mended. With Paris green the quantity was somewhat greater, 

 ranging from a minimum of one-half of a pound to a maximum of 

 one pound. 



In mixing the poison, flour and water, a large galvanized iron fun- 

 nel of thu'teen quarts capacity, having a cross septum of fine wire 

 gauze, and having also vertical sides and a rim to keep it from rock- 



