232 Alfred J. Ewart : 



In all cases, therefore, apples are much more sensitive to poisons 

 than potatoes. The cells of the latter are undoubtedly more 

 actively living, as is shown by the power of forming cork across 

 a cut surface, which the pulp cells of the apple are unable to do. 

 The latter are adult cells, Avith only a thin lining layer of living 

 protoplasm, specially adapted for prolonged existence in a more 

 or less statical condition, cUiring which their equilibrium is very 

 easily upset by the merest trace of poison. A high temperature 

 affects the sensitivity of potatoes to poison in the same way as it 

 does apples. 



Poisoning Theory of Bitter Pit. 



Rothera and Greenwood^ have recently made an attempt to 

 obtain a direct answer to this problem. They found in the first 

 place that starch grains from both pitted and normal apples woidd 

 dissolve in diastase, but that in some cases starch grains might 

 still be undissolved after 10 days, thus confirming the results ob- 

 tained by me in 19122, which also showed that resistant grains 

 will usually dissolve after treatment with dilute hydrochloric acid, 

 for a reason to be given later. In regard to the cell-wall, misled 

 by McAlpine's statement (1st Report, p. 12), that the brown colour 

 of bitter pit is due to a gummy or mucilaginous substance of a 

 pectic character, which colours the cell-walls brown, Rothera and 

 Greenwood investigated the chemistry of the cell-wall, and could 

 find no pronounced indication of a difference of composition be- 

 tween the cell-w^alls of healthy and pitted tissue. This is not sur- 

 prising, since the brown colour is due to the formation of an 

 oxidation product of tannic acid which unites with the protoplasm 

 lying within the cell-wall. In the early stages of bitter pit the cell- 

 wall is colourless and unaltered. Any changes in the cell-wall could 

 only be the result of slow impregnation subsequent to death. 



Direct tests of the poisoning theory of bitter pit w^ere performed 

 by adding the insoluble ash of bitter pit, and the portion dis- 

 solving in 10 per cent, nitric acid to starch — diastase solution- 

 No poisoning action could 1)0 detected as compared with controls. 

 This is hardly surprising. One experiment only was performed 

 with bitter pit material, which had been mixed with sand, tri- 

 turated and used for the extracton of starch. It had, therefore, 

 already been washed, and was again well washed with water, 

 alcohol and ether. The possibility of poisons l)cing washed out 



1. Chemical investiffation on Bitter Pit, 1913. 



2. Proc. Roy. Soe. of Victoria, vol. xxiv. (n..s.), p. 41o. 



