THE CAUSE OF BITTER PIT. 75 



The concentration of the cell-sap is therefore, in all probability, the immediate cause, acting 

 directly upon the protoplasm, and it must not be forgotten that this concentration is increased by an 

 insufficient supply of water as well as by excessive transpiration. How this loss of water is brought 

 about in isolated patches requires explanation. When there is an even flow of sap the loss of water by 

 transpiration is regular and continuous, but when there are violent vicissitudes in the weather the sap 

 flow becomes irregular. The growth of the apple will therefore vary, and when the growth becomes 

 too rapid for the delicate network of vessels surrounding the pulp to keep pace with it, meshes of the 

 net here and there are not formed, and the loss of water at these spots cannot be fully met by a fresh 

 inflow of sap. This loss of water without a corresponding supply causes the cells to collapse, and the 

 oxidizing enzyme in the presence of tannin turns them brown. 



In the above view the loss of water in localized spots is accepted as the primary cause of the 

 disease. But it is also possible that the loss may be a consequence of the death and collapse of the 

 cells, and this alternative view will now be considered. 



Undue pressure of water in the tissues beneath the skin, as evidenced by the gaps in the 

 meshes of the vascular network where Bitter Pit occurs, might conceivably cause the death of the 

 cells, and the subsequent deficiency of water would be a post mortem appearance. There are 

 various facts which strengthen this view. 



In the case of very rank growth of fruit on a young tree bearing only a few apples, as shown in 

 Figs. 27, 28, the conditions are most favourable for the development of Pit, and in this instance every 

 apple was pitted. There is an excess of water in the tree as well as in the fruit, that is to say, more 

 water is received from the roots than that given off by transpiration. But with the rapid growth of the 

 fruit there is excessive transpiration from its surface, and it is only when the amount of transpiration is 

 relatively greater than the water supply that Bitter Pit is produced. Where there is a strong flow of 

 sap, as in the young fruit-bearing tree or in older trees when the fruit is mostly confined to the main 

 branches, there the Pit is increased. On the other hand, when the flow is checked by cincturing, the 

 Pit is reduced, and it would seem that the over-pressure of water in a variety unable to withstand the 

 strain might be the exciting cause. 



This extra pressure would probably lead to death by the rupture of the cells and produce the 

 characteristic appearance of Bitter Pit. Although it has been shown that the dead pitted cells may 

 again take up water, this absorption may be a purely physical phenomenon, as in the case of blotting 

 paper. That Bitter Pit appears in the first instance immediately beneath the skin would favour this 

 view, since the external layer of the pulp-cells would be most subject to sudden fluctuations in their 

 water content, and a sudden access of water would cause excessive turgidity at localized spots. 



The rapid transportation and production of soluble substances in the cell-sap of the growing 

 fruit would also affect the result. The osmotic absorption under such circumstances must be very 

 rapid and the strain set up very strong. 



In either case the outstanding fact remains, that attacks of Bitter Pit are most virulent where 

 the sap flow and transpiration are subject to violent vicissitudes. 



Hence Bitter Pit is ultimately traceable to the varying nature of the climate and to a certain 

 extent to the nature of the variety itself. 



Fortunately, in the case of Bitter Pit other factors than the weather enter into the problem, 

 and it is by the control which the intelligent orchardist can exercise over the growth of the tree and 

 the formation of the fruit that the disease can be kept within manageable limits. When the fruit is 

 removed from the tree we can still prevent the development of the disease by means of cold storage. 

 And even when the difficult problem of altering the constitution of the tree has to be faced, we can still 

 adopt the slow but sure process recommended in a letter to me, under date February, 1915, from 

 Luther Burbank, the foremost plant-breeder in the world : "From your report I am more than ever 

 convinced of what I have long believed, that all fruit diseases and defects must in the end be bred out 

 of them, rather than combated in varieties which are susceptible to them." 



