492 EXPERIMENTAL FARMS 



4 GEORGE V., A. 19U 



allowed to drain for a moment. Portions of the spotted skin were removed with sterile 

 forceps, and the tissue underlying the spots transferred by means of sterile forceps or 

 scalpel to Petri dishes. Tissue transfers were made from all sizes of spots from the 

 smallest to the largest. In the former, as already mentioned, the discolouration did 

 not always go through the skin and therefore some cultures were also made with 

 portions of the spotted skin. One or two large spots which had been observed to be 

 enlarging were also used, as they seemed to have started from the 'typical spots. Plates 

 were poured with nutrient agar and 20 per cent potato agar. After six" days the cul- 

 tures taken from the enlarging spots showed a plentiful growth of mould (Penicil- 

 lium). Those in which the skin of the apple had been used showed in some cases a 

 growth of moulds; presumably the sterilization of the surface had not been complete. 

 None of the other cultures, however, showed the presence of any organism nor did 

 any develop later. 



It seemed therefore from the non-enlargement of the spots when kept either at 

 room temperatures or just above 0° C, together with the failure to develop organisms 

 from them, that the cause was not a parasite. At the same time it seemed probable 

 that saprophytic fungi could obtain entrance through these spots and set up rapid 

 decay. Our correspondent evidently suspected arsenate of lead as a possible cause, 

 and an account of a spotting of apples suspected to be due to this cause has been 

 published. ('A new fruit spot of apple' by W. M. Scott, Phytopathology I., 32-34.) 

 As compared with the spotting described by Scott, it would seem that the case under 

 consideration differs in the much greater number of the spots, their small size and 

 their absence from the ' blush ' side instead of being concentrated there. If, how- 

 ever, the spotting is due to soluble arsenical compounds in the spray mixture, it is 

 rather to be expected that the effect, as in this case, would be greater on the side 

 away from the sun as evaporation would be slower and the chemical have a longer 

 time to act. The spots being. so small, a reliable comparative analysis of spotted 

 and unspotted portions of the skin would have been somewhat difficult but an analysis 

 of the skin as a whole, kindly made by the Dominion Chemist, Mr. Shutt, showed 

 arsenic to be present to an average extent of -00083 milligrams per apple. 



It may seem at first sight that a spotting of the fruit which has developed in 

 storage can hardly be due to the use of arsenical sprays applied when the fruit is 

 not yet mature. It was shown, however, as stated, that arsenic was present on the 

 skin of the apples when examined. It is possible, therefore, that the changes under- 

 gone by the apple in the process of after ripening may result as Waite* has suggested 

 in the excretion of organic acids which have dissolved enough of the adherent 

 arsenic to kill the adjacent cells. On the other hand Ewart** has shown that the 

 pulp cells of an apple become increasingly sensitive to minute quantities of certain 

 poisons as the fruit matures, and that the cells on the shaded side are more sensitive 

 than those on the side exposed to the sun. He has, therefore, suggested the possibility 

 of poisons being absorbed in minute quantities into the tissue of young apples but 

 not producing any effect until the cells have been rendered more sensitive in the 

 process of maturation. 



At all events, while the cause of the spotting has not been demonstrated, it 

 would seem to be of non-parasitic and external origin and to have much in common 

 with the so-called ' Jonathan spot ' which is suspected to be due to the use of 

 arsenate of lead as an insecticide. 



* Quoted by W. H. Soofct, i.e. 



** Ewart, A. J., on Bitter Pit and the eensivity of apples to poisons. Proc. Roy. Soc. 

 Victoria 24 (N.S.) Pt. II, 1911. 



