16 Alfred J. Ewart : 



tissue, an increase of osmotic pressure simply causes the cells to 

 ^jress more firmly against one another and the tissue expands as a 

 whole, sometimes leading in the case of thin-skinned apples floated 

 on water to the bursting of the outer skin, but not to a bursting of 

 the pulp cells. A bursting of the outer skin does not accompany 

 the development of Bitter Pit, which on this theory it should do. 



In addition apple pulp may be immersed in water without the 

 cells being at first injured or bursting. Later they may die and 

 brown, and in soft fleshed apples the pulp cells may separate singly 

 or in clusters, but again without bursting, although here the supply 

 of water is greater than ever exists when the fruit is on the tree. 

 Both the bursting and the vascular interruption theories fail 

 entirely to take account of the actual sequence of events in the 

 development of Bitter Pit. In the early proteid stage of the apple, 

 no signs of the disease are shown. During the starch stage, in 

 certain localized areas the starch grains remain undissolved in 

 groups of cells, which are at first colourless and living. These cells 

 later die. turn brown and may collapse or shrivel. The first 

 symptom of the disease is the non-solution of the starch grains. Now 

 to prevent a dry starch grain from absorbing water a pressure of 

 2500 atmospheres is necessary, so that a pressure at least approach- 

 ing this would be necessary to prevent it dissolving under the action 

 of an enzyme, such as diastase, which cm only act in the presence of 

 water. Tlie maximum pressure of the ascending sap is less than 

 1 atmosphere and tlie maximum osmotic pressure in apple cells con- 

 taining 10-15 per cent, of sugar is 12 to 20 atmospheres. It is well 

 known that in cells with quite as high osmotic pressures as this 

 starch grains dissolve readily, and actual tests have shown that 

 bitter pit tissue is more deficient in sugar than the ordinary pulp, 

 which is the direct result of the non-solution of the starch grains. 

 To invoke changes of sap pressure or of osmotic pressure as a cause 

 of bitter pit is therefore a transparent absurdity. 



Mr. McAlpine (p. 73) states "the theory of spraying with 

 poisonous compounds w-as brought forward as a direct and definite 

 cause. That theory has now been abandoned and the absorption 

 of poison from the soil in infinitesimal quantities through the roots 

 substituted for it." In justice to Dr. White who first put forward 

 the poisonitig theory of Bitter Pit, so misleading a statement can- 

 not be allowed to pass uncontradicted. In the paper in question'^ 

 Dr. White sums up in the following words : " The results of my 



1 Proc. Roy. Soc. Victoria, 1911, p. 16. 



