28 Alfred J. Ewart : 



parts or organs, particularly such as are ultimately rliiown off 

 (leaves, bark, fruits), without either the roots or the plant as a 

 whole being affected. The following poisonous metals may l)e 

 absorbed by various plants when grown on soils containing them : 

 Zinc up to 13 per cent, of ash, manganese up to 14 per cent., 

 cobalt, nickel, mercury, silver, copper up to 1 per cent., lead, 

 thallium, arsenic, titanium, etc. These absorbed poisons arc either 

 set aside in special parts or cells sacrificed as poison traps, or may 

 not cause any injury at all if the plant has developed the power of 

 precipitating them in an insoluble or innocuous foi'm. 



Actual tests with the roots of seedling apples showed (with sul- 

 phate of copper) a toxic limit lying between 1 in 100,000 and 1 in 

 500,000, although when transpiration is active the limit may be 

 lowered, while when growing in garden soil seedlings may be 

 watered with much higher concentrations without being appreciably 

 affected. In the case of Yates' Pippin the toxic limit of the pulp 

 cells (1 in 1,000,000), is not much lower than that of tlie roots, 

 which may explain why this variety is practically immune to bitter 

 pit, Avhereas in the varieties more sensitive to poisoning and to 

 bitter pit, the ultimate toxic limit may be 100 times lower than for 

 the roots, which allows an ample margin for differential pidsoning. 

 The pulp cells are end points where poisons may accumulate until 

 a toxic limit is reached, and tliis toxic limit falls with increasing 

 age or rising temperature. In addition waste and ])oi.soiious sub- 

 stances frequently tend to accumulate and concentrate in particular 

 cells or groups of cells which are sacrificed for the benefit of the 

 rest. Evidence has already Vjcen brought forwaid to show t.Iiat this 

 occurs in the apple. 



Some of the experiments Ijrought forward to show the absence 

 of any connection between spraying and bitter pit are worthy of 

 comment (Report p. 23). In a Deepdenu orchard, wla-ic twelve 

 trees were to have been cut down on account of bitter pit, these 

 were reserved, and left unsprayed. As the result a total of 23j lbs. 

 of fruit were formed, including twelve apples affected by bitter pit. 

 So that, apparently, if the experiment indicates anything, it shows 

 that the absence of one yeai's spraying reduced the bitter pit 

 apples to one per tree ! 



At Burnley Gardens some fruits were enclosed in Ijags and othois 

 left exposed on an unsprayed tree of Annie Elizabeth. Of the 

 apples enclosed in bags 55 per cent, were pitted, and of the exposed 

 one 39 per cent. Calico bags were used, however, and as calico 

 glazes sometimes contain zinc oxide and other metallic poisons, it 

 would be interesting to know whether the bags were tested before use. 



