418 Alfred J. Ewavt : 



substances which decrease the percentage of free ions, and oa 

 these lines it may be possible to modify even such relatively 

 insoluble spray poisons as Bordeaux mixture and arsenate of 

 lead, without appreciably affecting their value as insecticides 

 and fungicides. Zinc arsenite has been recently suggested as 

 being equally effective as an insect poison, and less poisonous to 

 plants than lead arsenate. 



Nevertheless since the fungus, Penicillium, which is a com- 

 mon cause of wet rot in apples is able to grow on a 20 per cent, 

 solution of copper sulphate, it is 2,000,000,000 times more 

 resistant to copper than the pulp cells of apples, and it is also 

 very much more resistant to mercury saltsl. Jq this case 

 " fungicides " will kill apples long before they kill the fungus. 

 Of gases present in the air, ozone, ammonia and nitric acid are 

 able to produce surface pitting in apples, but only in amounts 

 and with lengths of exposure relatively much greater than those 

 presented under ordinary conditions. 



Five milligrams of solid iodine placed a foot distant from an 

 apple can cause* it to become covered with spots and pits in the 

 course of time. 



Apples absorb and accumulate arsenic from arseniuretted 

 hydrogen, a strong poisonous action being exercised when a con- 

 centration of 1 of arsenic trioxide per 500,000' of apple pulp is 

 reached. When once within the pulp cells, lead arsenate i» 

 poisonous in a concentration of 1 in 13,000,000. 



Tlie following results conclusively show that the "' disease ' 

 of apples known as bitter pit is, strictly speaking, not a 

 " disease '* at all, but is a symptom of local poisoning. 



Bitter pit symptoms, including the presence of abundant 

 starch grains in dead cells, are frequently shown in the spots 

 appearing on peach and apple foliage, when burning is produced 

 by poisonous sprays. Not only arsenate of lead, but all the 

 other common spray poisons are effective causes of bitter pit 

 in apples. When the entry takes place from the surface of the 

 apple at the close of ripening, the pits are superticial and without 

 starch grains. The usual characteristics of bitter pit are only 



1 Penicillium can also withstand 15 per cent, of zinc sulphate, 37 per cent, of 

 manganese sulphate, 8 perjcent. of ferric sulphate and is also resistant to arsenic, all of 

 which are poisonous to ordinary plants. 



