Bitter Pit in Ajpples. 9 



Comparison of these two sp'raving materials, i.e., lead arsenate 

 and lead chromate, sIioavs tha-t the former is sparingly soluble in 

 water, whilst the latter is practically insoluble. As the injurious 

 effect of any poison depends on its solubility in the liquid 

 employed as a solvent, a perfectly insoluble compound, if such 

 exists, in water could not, if applied in water only, do any 

 damage. Both these substances are soluble in dilute vegetable 

 acids, so that if grains of the solid material happen to get into 

 the interior of the apple they might be dissolved by the acid 

 juice. Measurement of the orifice of a stoma shows that six 

 grains of lead arsenate abreast could enter the stomatal orifice. 



Comparison of the size of the grains of both materials in their 

 usual commercial foniis shows they are very similar in this 

 respect, but probably the majority of the chromate grains are a 

 shade larger than the arsenate ones. 



As the disease occurs principally in apples and pears, and as 

 these are the fruits which are particularly liable to be attacked 

 by the codlin moth, it seems to indicate that it is more especi- 

 ally the arsenical sprays which are employed for the destruction 

 of this pest which cause the damage to the fruits. 



Close obsen'-ation of those apple trees at Burnley which were 

 used for my investigations showed that whilst the pitting was. 

 practically always confined to the calyx end, it was almost uni- 

 versally more pronounced on that side of the fruit which was 

 not exposed to the sun's rays. (See Figs. 3 and 4.) Also the 

 fruits situated on the southern aspect were more affected 

 than those on the western aspect, whilst those on the northern 

 aspect were the least so. TTie first fruit to show indications 

 of the disease were those situated within easy reach, and these 

 were, as a rule, much more pitted than those growing above and 

 below them on the tree. All these facts point to spraying as 

 the cause of the trouble, for in the majority of cases the liquid 

 is sprayed straight on to the calyx end of the fruit, and the 

 inference is that those situated within easy reach of the sprayer 

 receive a larger dose. The water containing the spray material 

 soon evaporates from the surface of the fruit, that which rolls 

 down to tlie more shaded under side, being less quickly evapor- 

 ated, remains longer, and consequently this side of the fruit 

 would be more likely to become affected. 



