26 



This has always been the principal objection to the use of arseni- 

 cals, since foliage " burned" soon falls to the ground, and a tree 

 thus deprived of its leaves in the middle of a season is of course 

 unable to ripen its fruit or successfully complete the year's growth 

 of wood, and, in addition, is materially injured by the exhaustion 

 of the reserve force necessary to produce the second crop of leaves 

 which most species of deciduous trees bring forth when defoliated 

 early in the season. Thus the damage to the tree from "burning" 

 is often as great as that from defoliation by insects. The burning 

 effect on leaves of arsenical poisons depends on the destruction of 

 the living contents (protoplasm) of the cells which go to make up 

 the leaf, as is shown by the illustrations which follow. 



Fig. 1 (original). Section through normal 

 leaf of pig-nut hickory {Cart/a porcina), 

 showing structural elements. E, epider- 

 mii* ; PC, palisade cells ; S P, spongy paren- 

 chyma; S, stoma or breathing pore. 



Fig. 2 (original). Section through leaf of 

 same tree "burned" by excess of Paris 

 green. Cell contents (protoplasm) of pal- 

 isade cells and spongy parenchyma dead 

 and dried up; cell walls shrivelled. 



How TO USE THESE PoiSONS AGAINST CoMMON INSECTS. 



Spraying with a force pump is the best method of applying these 

 poisons to trees. It is well to add from two to four quarts of 

 glucose or cheap molasses for every one hundred and fifty gallons 

 of the poison mixture used, as this causes the poisons to adhere to 

 the foliage. To destroy the bud moth (Tmetocera ocellana)^ spray 

 when the buds begin to swell; against the codling moth {Carpo- 

 capsa pomonella) , spray just after the petals have fallen from the 

 blossoms. The tent caterpillar (^Clisiocampa americcma) ^ the 

 canker-worms {Anisopteryx jiometaria^ Paleacrita vernata), as 

 well as the tussock moth (Orgyia leucostigma) and the elm leaf 

 beetle {Galeruca xanthomeloina) can be cleared from infested trees 

 by one or more thorough sprayings soon after the insects make 

 their appearance. 



