1;> 



parts, for on cutting a ripe apple across, these spots frequently tend to 

 tear out wholesale when they meet with the knife edge. When a clean, 

 cut is made across one of these necrotic areas they almost invariably show 

 even to the naked eye a frothy or very spongy texture. The spots are 

 not confined to the periphery of the apple, but are distributed throughout 

 almost to the core (see Plate II). The external depression or pit is brought 

 about by the collapse and coalescence of the cells comprising the brown 

 tissue. Connected with these spots internally a discoloured vascular 

 bundle is nearly always found. If a thin slice of apple about an eighth 

 of an inch in thickness is taken and then left for a few days to dry, the 

 brown spots remain standing up prominently above the rest of the tissue, 

 clearly exhibiting the toughness and firmness of their composition, and 

 when examined with a lens the spongy meshwork is very evident. The 

 brown tissue is frequently found in apples which externally look quite 

 healthy. 



Microscopical Examination of the Brown Spots. 



When the brown spots are examined microscopically, they are found 

 to be composed of larger and thicker-waUed cells than occur in the healthy 

 tissue. A great nimiber of these cells are ruptured and broken down, so 

 that the opposite walls have collapsed and lie flat against one another, 

 and at the same time imprison mmierous starch grains between them (see 

 Plate III). These ruptured walls are coloured brown with a gummy or 

 mucilaginous substance, which is of a pectic nature, as is shown by micro- 

 chemical tests and stains. No evidence of lignification, cuticularisation, 

 or suberisation could be obtained. 



These waUs are not readily soluble in concentrated sulphuric acid, 

 nor are they stained blue or violet with iodine and sulphuric acid, or with 

 chloroidide of zinc. 



In tracing the development of these brown spots, it is found that they 

 always arise in close connection with the vascular bundles, and especially 

 at the ends of the bundles. The cells bordering on the bundles are the 

 first to enlarge and burst, as is seen in the micro-photographs. If a thin 

 shce of an affected apple is treated with iodine a distinct blue colouration 

 appears only in the neighbourhood of the spots, and this on closer 

 examination is seen to be due to the imprisoned starch grains within the 

 collapsed cells. A careful study of these starch grains reveals the fact 

 that they are part and parcel of the original starch formed in the cells, 

 and are not a secondary product resulting from the conversion of the 

 sugar into starch by any new growth such as sometimes occurs. The 

 establishment of this fact is of importance, as it proves conclusively that 

 the injury to these cells occurred before the ripening of the fruit. These 

 facts, together with the general appearance of the spots, leads me to 

 conclude that this unhealthy condition of affairs is brought about bv the 

 following sequence of events. The cells surrounding the vascular bundles 

 or those commonly situated at their ends are being continually subjected 

 to great internal pressure, with the result that they become enlarged and 

 thicker-walled. This internal pressure is undoubtedly due to an accumu- 

 lation of water, which inflates the cells to such a pitch that in many cases 



