THE CAUSE OF BITTER PIT. 73 



XV. THE CAUSE OF BITTER PIT. 



If an engineer has to repair some defect in the working of a steam-engine, he must overhaul 

 the machinery, and the more he knows about the structure of the various parts and the work they 

 perform, the better able will he be to determine the nature of the defect and the cause of it. Similarly, 

 if a medical man has to deal effectively with some disease of the human body, he must not only be 

 familiar with the structure and functions of the organ concerned, but he must also know its relations 

 with other parts of the body. He must be acquainted with the means whereby it is nourished in order 

 to perform its functions properly and the various arteries and veins, nerves and muscles connected 

 with it. He must also take into account the environment, which exercises such an important influence 

 on the harmonious working of the various factors. 



So, in dealing with this disease, our first efforts were directed to a thorough investigation of 

 the structure of the apple and the way in which this structure is related to the building up of a sound 

 and healthy, palatable, and succulent fruit. 



After this study of the apple in the normal condition of health, the way was prepared for the 

 study of the abnormal condition of disease, and the various symptoms of Bitter Pit were determined. 

 In seeking for the cause of this defect there were a number of theories which required to be examined 

 and tested in order to exclude those factors which are not concerned in it, and to narrow down the 

 probable causes as much as possible by the method of exclusion. Plants, or parts of plants, are often 

 subject to diseases due to invasion by parasites, which may deprive the plant of necessary food, inter- 

 fere with its proper water supply, or derange some vital function. Or diseases may arise from the 

 disturbance of function caused by external agents, such as the nature of the climate, soluble materials 

 in the soil, or gases in the air. 



It has already been conclusively shown that this is not a parasitic disease, and therefore not 

 infectious. The agency of insects, of fungi, and of bacteria has been excluded, and while this advance 

 has narrowed down the enquiry and made it easier, it has not removed all difficulties from the path. 

 In the case of a parasitic disease there is always a definite basis from which to start the study of the 

 parasite, its life history, and its mode of action. But when there are functional disorders, as in this 

 instance, without any definite clue to start from, the study becomes more difficult, and it is little wonder 

 that scientists have often spoken of "the mystery" of Bitter Pit. 



It is sometimes called a physiological disease to indicate that it is not parasitic in its origin, 

 but from the point of view of the nature of the disease itself this distinction cannot be strictly main- 

 tained. All diseases, however caused, are physiological in the sense that they are disturbances of 

 the normal physiological functions, but there is a certain convenience in retaining the term for non- 

 parasitic diseases. 



The same method of exclusion has been followed in dealing with external agencies as with 

 parasites. 



The theory of spraying with poisonous compounds was brought forward as a direct and definite 

 cause, and the general use of arsenate of lead for spraying in the treatment of Codlin Moth seemed to 

 favour this view. But it was at once pointed out that this disease was well known in Australia long 

 before spraying was adopted, and that it was very bad in districts of Western Australia where no 

 Codlin Moth existed and consequently no spraying for it. 



That theory has now been abandoned, and the absorption of poison from the soil in infinitesimal 

 quantities through the roots has been substituted for it. An experiment to test this theory was made 

 last season at Burnley Horticultural Gardens, and the results have been already given by Dr. Rothera 

 in his report. 



There still remain for consideration those diseases included under the general term of Necrosis, 

 from a Greek word meaning "dead." This applies to those cases where the tissues die and dry up, 



