70 



BITTER PIT INVESTIGATION. 



Next, the various theories propounded to explain the nature and symptoms of the disease 

 were considered in order to eliminate, as much as possible, unnecessary and irrelevant factors, and 

 to narrow down the issue within reasonable limits. It will be sufficient for our present purpose to 

 note the following as the principal causes assigned : — 



1. Acidity of the concentrated Sap. — The first really scientific investigation of the trouble, 

 which had long been known in Europe, was made by Professor Wortmann in 1892. His experiments 

 and observations led him to the conclusion that the death of the cells in the brown spots was due 

 to the concentration of the acid of the sap following upon the loss of water. In connexion with this 

 theory, Dr. Wortmann (97) states that it can easily be proved by experiments in which the contents 

 of the pulp cells are artificially concentrated. ■ For this purpose he recommends salt or sugar 

 solution in which punctured apples are placed, and he observes that in 24 hours sharply 

 circumscribed spots are produced. But the mistake was made here, as had already been done in 

 the case of citric acid (Fig. 57) of confounding superficial spotting with Bitter Pit, and this 

 was strikingly shown in repeating his experiments with salt and sugar solution and tap water 

 respectively. 



I took mature apples of the Yates variety, which are known to be practically immune to 

 Bitter Pit, and placed both punctured and unpunctured specimens in a 10 per cent, salt solution, 

 the same strength of sugar solution and tap water. 



Salt Solution. — In the unpricked specimen there was no change in 24 hours, but in the 

 pricked specimen there was a slight discoloration of the skin around the punctures, the spots being 

 about 5 mm. in diameter. The spots were sometimes isolated and sometimes run together, where 

 the punctures were in the form of a cross, so as to extend to one inch across. 



When cut across, the tissue beneath the spot is not discoloured, but spongy, crescent shaped, 

 and extending to the depth of the punctures. The portion affected beneath the skin is readily 

 detached from the surrounding tissue. 



Sugar Solution. — In the unpricked specimen there was no external change, but the pricked 

 specimen showed a slight discoloration around the pricks. The tissue beneath was practically 

 unchanged. 



Tap Water. — The most conspicuous spotting was produced by the tap water on the pricked 

 specimen, the unpricked remaining quite firm, and without any change. Some of the punctures 

 showed round discolorations up to 7 mm. in diameter, with very slight depressions or none at all. 

 When cut across the tissue is seen to be more watery to the depth of the puncture than that 

 surrounding it, and somewhat resembling " glassiness." The water had evidently penetrated 

 the punctures, and displaced the air in the tissue affected. 



2. Bursting and consequent breaking-down of certain cells of the flesh due to too great internal 

 Pressure. — This was the conclusion reached by Pole Evans as to the cause in 1909, after an 

 exhaustive histological and bacteriological examination. But it has already been shown that, while 

 the pulp cells have collapsed in the Bitter Pit spots, there is no evidence of bursting, and further, 

 the cell-walls pressing against each other would tend to prevent it. 



3. Spraying with poisonous Compounds. — This was the theory enunciated by Dr. Jean White 

 in May, 1911. It has not only been shown, however, that Bitter Pit had been known in Europe 

 and America, as well as in Australia, before spraying fruit trees for pests was introduced, but badly 

 pitted fruit has been obtained here from apple trees which were purposely left unsprayed. 

 Experimental and chemical evidence was brought forward to disprove it, and historical evidence 

 from Australia and other countries showed that the disease existed long before spraying with 

 poisonous compounds was thought of. 



4. Absorption of Poisons through the Roots. — This is the theory put forward by Professor 

 Ewart in a paper read before the Eoyal Society of Victoria on 14th December, 1911. This theory 

 is sufficiently disposed of by the analysis of pitted apples made by Mr. P. R. Scott, Chemist for 



