74 BITTER PIT INVESTIGATION. 



gradually becoming brown or black in patches ; and these dead patches sometimes spread slowly 

 and invade the surrounding healthy tissues. The name is usually applied in plant pathology to the 

 appearances presented by the slender stems or branches or thin twigs, and may be due to the action 

 of frost or sunburn or to the bruising of the tissues by hailstones. 



Bitter Pit in the fruit occurs in the absence of frost or hail, and sunburn or scorching is easily 

 distinguished, since it involves the skin as well as the underlying tissues. 



The action of hail, when not sufficiently strong to rupture the skin, might easily be mistaken for 

 Bitter Pit, since the pulp tissue immediately beneath the skin is brown and spongy. There is this 

 important difference, however, that Bitter Pit occurs without any such external injury to the fruit, 

 and the origin of the appearances must therefore be sought for from within. 



If pressure is applied from the outside of an apple by the rounded end. say, of a glass rod, so 

 as not to break the skin, some of the meshes of the vascular net are broken, and in the course of twenty 

 minutes the pulp-cells beneath the skin at that point are collapsed and brown, just as in Bitter Pit. 



This brings us to the point where the origin of Bitter Pit may be profitably discussed, since here 

 also the vascular network is interrupted wherever the brown flecks in the flesh occur. 



In dealing with the causes of disease, we have always to consider those of a general nature 

 as well as those which are special in their character. 



All sorts of general statements are made as to the cause of Bitter Pit, and there is a certain 

 amount of truth in many of them. It is said to be due to disordered nutrition, and the affected pulp- 

 cells bear evidence of interference with the normal functions. Dr. Rothera has pointed out that Pit 

 has always been associated with starch in his experience, and that the critical time for the apple is 

 when the pulp-cells are loaded with starch and before the starch has been converted into sugar. It 

 is only when the insoluble starch is converted into soluble sugar that it can be assimilated, and whatever 

 prevents this interferes with the process of digestion. In ninety-nine cases out of a hundred starch 

 is present in the cells of the pitted tissue, so that "starch metabolism and Pit are evidently closely 

 associated" is the conclusion of Dr. Rothera. 



Again, it is said to be a disease of the vascular or conducting system, and no doubt the vessels 

 are involved. It is in the neighbourhood of the vessels that the disease begins, and they become 

 discoloured like the affected pulp-cells. 



Further, a superabundance of sap is said to cause it, and it is often in the overgrown apple 

 that the disease manifests itself. A striking illustration of this was given in Report II., p. 42, where, 

 in a Western Australian orchard, Cleopatra trees only showed Bitter Pit in the clusters of fruit at the 

 tips of the branches, and the larger apple in the centre of the cluster was the worst. It is well known 

 that the highest or terminal bud receives the largest amount of sap, and so constant is this that during 

 one season I was unable to find a single instance of the unusual case of the smallest apple being in the 

 centre among all the numerous trees in the Burnley Horticultural Gardens. 



Finally, it is said to be a constitutional disease, and when one considers that the plump, 

 succulent, and sweet cultivated apple has been derived from the small and sour crab, and that in this 

 process the hardy nature of the ancestor has been sacrificed, particularly in the direction of a softening 

 of the fibre, it must be confessed that the penalty paid for the increased attractiveness is a weakening 

 of the constitution. 



Our present knowledge does not, in my opinion, warrant dogmatism as to the cause of Bitter 

 Pit, but after a close study of the structure and functions of the tissues of the fruit, and after excluding 

 a number of supposed causes found to be no longer tenable, I have come to the following conclusion 

 as to the immediate cause : 



In Bitter Pit tissue the pulp-cells have collapsed, and the brown flecks in the flesh contain 

 much less water than the neighbouring healthy tissue. Owing to this loss of water, the acids and other 

 constituents of the cell -sap have become concentrated, and the amount of concentration reaches a 

 point where the living substance of the cells is injuriously affected, and finally death ensues. 



