10 BITTER PIT INVESTIGATION. 



The notes of experiments show only eight as developing marked Pit. 



This means, that in order to detect the earliest evidence of Pit at that initial stage, before there 

 is any depression of the skin, or browning of the affected cells, 50 apples must be gone over section 

 by section with some test capable of unmasking the Pit and as yet that test is not discovered. 

 The explanation of the low incidence of the disease in the laboratory-kept apples is : 



(a) That many of the clean apples came out of cool storage late in the 1914 season, when 

 all fruit, which was to Pit had already done so, and only the really clean fruit 

 remained with a clean appearance. 

 (6) That even with the fruit received in the height of the 1915 gathering season, the fruit 



was showing some signs of the disease, if about to pit, or else was actually clean. 

 In short, the period of Pit incidence had occurred before the fruit reached the laboratory in 

 all but a very small minority of the apples received. 



The material required was clean fruit from a single tree, with a bad reputation for Pit. The 

 appearance of Pit on the tree marked the clean fruit, as that which was most likely to be of interest. 

 Yet, in only the brief week or two of the harvesting season was clean fruit obtained which pitted 

 under observation. Other supplies, which had been especially put aside in cold storage, emerged 

 either permanently clean or pitted.* 



One fine supply of Rome Beauties arrived in a condition in which to the casual observation 

 thev appeared clean. But there was a just perceptible mottling in darker green, and on peeling it 

 was obvious that this mottling was due to Pit. Out of 84 apples 50 were at once grouped as pitted, 

 and of the other 30 only 6 were actually clean. 



Consequently one feels that the determination of Pit or no Pit occurred prior to the apples 

 reaching the laboratory. 



THE EARLY DETECTION OF PIT. 



Considerable attention was directed to this point, but it must be admitted that no actual 

 results were obtained, and from what is now known this was almost inevitable. 



(a) From the work having been for the most part carried out on unsuitable material ; 

 (6) From the insufficient mass of material examined ; 

 (c) From the considerable experimental difficulties. 



The methods by which the problem may be attacked can, however, be discussed, and the 

 difficulties met with may be stated, in order to clear the ground for future work. 



MICROCHEMICAL METHODS. 



One of the most striking pictures of Bitter Pit is afforded when an affected apple has the peel 

 removed. In a badly diseased apple the whole peeled surface appears studded with small brown 

 areas of dry and shrivelled cells. As the affected tissue is more abundant towards the periphery of 

 the apple, it is just under the skin that the bulk of it is seen. 



It is also just under the skin that one would naturally look for Pit by special microchemical 

 methods in apples apparently clean, but possibly doomed to Pit on being kept. 



(a) STAINING METHODS DEPENDING ON ENZYMES. 



Reagents which colour under the influence of oxidase enzymes were applied uniformly 

 to the surface of apples which had been peeled. Para-phenylene-diamine (without 

 hydrogen peroxide), and tincture of Guiacum (with or without hydrogen per- 

 oxide) were used. In all cases uniform and good staining was obtained with no 

 indication of localised areas with excess, or defective oxidase enzymes. Results 

 were therefore negative. As later experiments showed the material used was 

 unsuitable. By this is meant that subsequent evidence indicated that the fruit 

 was in reality clean, and not in all probability with any latent Pit present. Methy- 

 lene blue was also tried for the presence of reductase. No evidence of such a 

 ferment was obtained. 



*Mr. McAlpine informs me that no separation of clean and unclean apples was made prior to the cold 

 storage. Cases of apples (the apples all from a single Annie Elizabeth tree) were placed in the Cool Store in the 

 condition as gathered. 



