60 BITTER PIT INVESTIGATION. 



The further investigations which I have subsequently been able to make into the occurrence of 

 Pit lead me to abandon an undue concentration of the cell sap as the probable cause of the disease. 

 I am of opinion that over-pressure of water in the tissues, leading to local rupture and subsequent 

 death of the parts, furnishes the most probable explanation of Bitter Pit. 



Histological examination of the tissues of the apple, and the results of field experiments, pruning 

 tests, and climatological observations concur in supporting the view that over-pressure of water is the 

 real cause. 



The diminished supply of water in the flecks of Bitter Pit is the result of cell rupture and death 

 of the parts not its cause. 



The following observations support this view : 



1 . When the apple fruit is mostly confined to the main upright branches and produced on 

 fruit-spurs, the Bitter Pit is usually increased. Under these conditions the strong flow 

 of sap might reasonably be supposed to burst the thin walls of the pulp-cells and produce 

 the effect. 



2. In a young and vigorous growing tree, bearing only a few apples of rank growth, all the 

 fruit is often pitted (Report IV., Figs. 27, 28). The rank growth will cause rapid tension 

 of the cell wall, and this may reach the breaking point, when the pressure is distributed 

 only through a few apples. 



3. When a tree in full bearing has only a light crop, and the apples are comparatively large, 

 then the tendency to Bitter Pit is greater. The fewer apples in this instance would 

 get a larger proportion of sap, as evidenced by their larger size. Instances have already 

 been given where 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 invariably 

 the worst. Superabundance of sap is associated with the over-grown apple and the 

 development of Pit. 



4. When the fruit of a susceptible variety is picked and graded, it is found, as a rule, 

 that the larger the fruit the more liable it is to Pit. Thus, in the produce of 39 

 Cleopatra trees, while apples two inches in diameter had only 1 per cent, of Pit, those 3| 

 inches in diameter had 61 per cent, of Pit. The greater growth in the larger apple 

 relatively to the smaller would tend to distend the pulp-cells and ultimately burst them. 



i>. When the strong flow of sap is checked by cincturing it is found that the Pit is reduced. 

 This favours the view that the over-pressure of the sap in a variety unable to withstand 

 the strain may be the exciting cause. Root-pruning is a well-known means of checking 

 growth and inducing fruitfulness, but owing to the danger in our variable climate of 

 root-pruned trees suffering from a diminished water supply at a critical period of their 

 growth, no satisfactory experiments were carried out. 



6. Irrigation experiments bear out the view that over- watering is a sure means of producing 

 Pit. When apple trees are heavily watered, and particularly late in the season when the 

 fruit is approaching its full development, there is a much higher percentage of Pit than 

 when light watering is adopted. 



7- When the fruit is produced on laterals where every apple, as a rule, has room to develop 

 properly and there is no strong flow of sap as in the upright branches, the amount of 

 Pit is appreciably lessened. 



8. As shown in a previous Report, wherever Bitter Pit occurs, the vascular network at the 

 boundary between the pulp-cells and the skin is ruptured. The pressure exerted will 

 also be sufficient to burst the adjoining pulp-cells, and thus there is strong presumptive 

 evidence that the bursting of the network by over-pressure of the water, more 

 particularly towards the apex or eye end of the apple, is accompanied by the rupture 

 of the pulp-cells. 



This is appropriately called a constitutional disease, since the root of the trouble really lies in 

 the artificial nature of our modern apple. It has been derived from the small, sour, and hardy Wild 

 Crab, and the large size, the succulence, and the sweetness have been obtained at the expense of the 

 hardy nature of its ancestor. The fibre is now soft and flabby to render the flesh as juicy as possible, 

 and this weakening of the fibre has practically thrown the whole burden of the skeleton upon the pulp- 



