VARIOUS CAUSES ASSIGNED FOR BITTER PIT. 



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In the light of our present knowledge of the structure and functions of the apple, and of the 

 different part3 of the tree itself, let us now see how these various theories as to the cause of Bitter 

 Pit stand the test. 



First, the essential point in Dr. Wortmann's theory is that concentration of the sap, 

 following the loss of water by transpiration, occurs in the pulp cells adjoining the vessels, and the 

 acidity of the concentrated sap is the direct cause of the injury. He maintains that this can be 

 easily proved by artificially concentrating the contents of the pulp cells by means of such re-agents 

 as salt or sugar solutions. He produced a kt spotting " of the skin, especially where it was punctured 

 to allow of the ready access of the solution to the interior, but, as already shown, this has no 

 relation to Bitter Pit. In fact, tap-water alone produced the most conspicuous " spotting," and 

 Dr. Wortmann has failed to show that concentration of the sap will account for the internal brown 

 spotting of the fruit. 



Second, Dr. Zschokke agreed with Dr. Wortmann that the death of the cells occurs in the 

 neighbourhood of the vessels, and is brought about by the gradual concentration of the cell-sap. 

 But, in order to account for the irregular distribution of the internal brown spots, he added an 

 additional factor to those brought forward by Dr. Wortmann, viz., the unequal distribution of the 

 water in the interior of the pulp. Certain groups of cells more favorably situated than others for 

 the conduction of water lost it more readily, and so the concentration of the sap and the consequent 

 death of the cells occurred there earlier. There is no reason given here why one portion of the pulp 

 should have a better or worse water supply than another. 



Third, since Massee based his conclusions on the examination of specimens sent from the 

 Cape, and not from observing the disease in the orchard, they have not the same wide significance 

 as in the two preceding cases. He considered that the fruit had been subjected to too high a 

 temperature at the period of ripening, and consequently certain groups of cells were killed by 

 fermentation. He very ingeniously explained the occurrence of the rusty dead patches beneath 

 the skin, because starch is most abundant towards the periphery of the apple, and so fermentation 

 would begin there before the starch was converted into sugar. The disease as it appears on the 

 trees is not dealt with here at all. 



Fourth, the latest important theory is brought forward by Pole Evans, who ascribes the 

 disease to the " bursting and consequent breaking-down of certain cells of the flesh, due to too great 

 internal pressure." This internal pressure is supposed to be brought about by the accumulation 

 of water in the pulp cells. Now it is difficult to see how the cells could be brought to the bursting 

 point since they possess such a capacity for expansion, and even when stretched to their fullest 

 extent the water can still exude. This will be made evident by one or two illustrative examples. 

 When a leaf begins to wilt, it is owing to the failure of the water supply, and the cells become flaccid 

 and collapsed. But when water is supplied in the form of rainfall or artificial watering, the leaf 

 stiffens, owing to the cells becozning turgid and distended, like so many puffed-up little balloons. 

 Of course, the excess of moisture here will be regulated by the amount of evaporation going on, 

 but still the capacity for extension of the cells is great. However, even if transpiration is kept in 

 check, as it is in the conditions under which Bitter Pit is supposed to occur, and there is great 

 pressure exerted on the cells, exudation may occur, and the pressure be relieved, as in the case 

 of Glassiness." Pole Evans himself says of this disease, " it is undoubted evidence of water 

 exudation under pressure. The cell sap fills the cells to overflowing, but, instead of bursting 

 them, quietly diffuses through their membranes or walls, and then accumulates in the intercellular 

 spaces." There is no evidence brought forward to show how the bursting of the cells bordering 

 on the vascular bundles should occur at one part of the apple more than another, as the cell- 

 walls press against each other, and thus prevent the rupture of the individual cells, or why the 

 disease of Bitter Pit should originate just beneath the skin. It will subsequently be shown that 

 it is collapse and not rupture of the cells which occurs in Bitter Pit. 

 C.1040U, K 



