62 



BITTER PIT INVESTIGATION. 



Having passed in review the various agencies brought forward to account for Bitter Pit, the 

 way is now clear for a consideration of other theories which more or less adequately explain it. 

 And among these they may be narrowed down to a very few, which are the result of painstaking 

 work, and which offer a reasonable solution of the problem. The first really scientific attampt was 

 made by Wortmann (97) in 1892, in his article, entitled "Ueberdie sogen. c Stippen ' der Aepfel" 

 (on the so-called " stippen " or " spotting " of the apple). Then Zschokke (98) in 1897 confirmed 

 and extended his work in " Stippigwerden der Aepfel " (spotting of the apple). Next Massee (54) 

 made a slight contribution to the subject in 1906, in his " Apple Disease " in the Kew Bulletin, and 

 finally Pole Evans (31) in 1909 gave the most plausible explanation and one which has received 

 general acceptance in his Technical Bulletin on " Bitter Pit of the Apple." As a result of these 

 various investigations, and with the additional knowledge gained of the minute structure and 

 functions of the apple and pear, I will be able to give such a view of the origin and development of 

 Bitter Pit as seems to me the most probable and most reasonable, and which will enable us, from 

 the solid bedrock of established fact, to proceed to practical measures for its control, or, at least, 

 mitigation. 



Wortmann's paper leaves no doubt that he is dealing with the disease of the apple now 

 known as Bitter Pit, both from the description of its general characters and the microscopic 

 appearance presented by the internal brown spots. He states at the outset that it is extremely 

 common, and, therefore, well known to the orchardist, and that it first appears at or subsequent 

 to the ripening of the fruit. In Germany it only appears exceptionally when the fruit 

 is on the tree, and then only in very liable varieties, shortly before the fruit is picked, and 

 in overgrown specimens. He observed that in the contracted and browned cells there were 

 small starch-grains, while in the surrounding healthy tissue they were either absent or very 

 scarce. He arrived at the conclusion, as the result of his researches, that neither fungi nor 

 bacteria are concerned in it, but that it is due to physiological causes. The spots did not 

 originate at the surface and extend inwardly, but they arose as isolated patches in the pulp 

 near the surface, and gradually extended to the skin, meanwhile blending with one another, 

 and forming larger spots. In seeking for their mode of origin he found that they were 

 always in direct relation to the branches or ends of the vascular bundles permeating the 

 pulp, and that they first appeared as pale brown groups of cells directly adjoining the 

 brown-coloured vessels. 



He, therefore, came to the conclusion that the brown spots stood in direct relation to the 

 conduction of water, and, indeed, with its diminution and final cessation, due to the plucking and 

 storing of the fruit. 



His experiments and observations led him to conclude that the death of the cells in these 

 spots is due to the concentration of the sap, following the loss of water. This loss of water, by 

 direct transpiration from the superficial cells, is soon followed by conduction of water from the 

 deeper-seated cells, and the consequence is that the concentration of the sap occurs in the pulp 

 cells adjoining the vessels. The acidity of the concentrated sap is considered to be the direct 

 cause of the injury, and this injury is followed by the browning, through oxidation, of the cells, 

 which have lost their water, and become dry. 



Several factors may, therefore, enter into the problem of the formation of the brown 



spots. 



1. The Amount and Rapidity of Transpiration. — This is influenced by the character of 

 the epidermis, conditions of storage, &c. It is pointed out that if the epidermis 

 is so constructed that it retards transpiration, Bitter Pit will be prevented or 

 only appear late, whereas, if it is easily permeable, the pitting will be readily 

 induced. The examination of the epidermis in liable and non-liable sorts bore 

 this out. 



