12 



BITTER PIT INVESTIGATION. 



If a thin transverse section of a pitted apple is taken about the equator, and stained with 

 various re-agents, the reactions of the different tissues or portions of them are shown. 



(a) Chlor-zinc-iodine, or Schulze's Solution, stains the starch-grains blue, and it is 



observed that the blue colour first appears around the ten fibro-vascular bundles, 

 and gradually extends outwards in a radiating manner, so that there are 

 ten radiating blue bands extending from the boundary of the core, indicating 

 the presence of starch. There are blue patches, more or less irregularly, through 

 the flesh, and some very deep blue lines immediately beneath the skin. The 

 brown spots in the pulp also contain starch, and are stained, but the brown 

 colour of the walls masks it somewhat. 



(b) Phloroglucin, with hydrochloric acid added, stains the lignified or woody tissue a 



rose-pink or even crimson, and the sections show the walls of the seed-vessels, 

 a circle of five dots at the very centre, and any portions of the fibro-vascular 

 bundles a beautiful pink colour. The brown spots only show- traces of pink, 

 where a portion of a fibro-vascular bundle is present, and there is no lignification 

 of the brown walls. Aniline sulphate has the same effect, only it stains the 

 lignified parts a bright canary yellow. 



(c) A freshly-prepared and concentrated solution of chlorophyll was also used to stain 



a section. After being kept in the dark for some time, a microscopic examination 

 showed no deep-green staining of the brown cell-walls, indicating that the walls 

 are not corky. Sections of cork treated at the same time showed the cell-wall 

 coloured a distinct dark-green. 



Thus, there is no evidence of the walls being lignified or corky, and the gummy or 

 mucilaginous substance which colours them brown is of a pectic character. 



When a ripe apple is selected, affected with Bitter Pit, the healthy cells are free from starch, 

 since it has all been transformed into sugar in the process of ripening. But the cells constituting 

 the brown spots contain numerous starch-grains, because the browning, and consequent death of 

 the tissue had occurred before the final stage of ripening had been reached. This is very evident 

 on examining a section of a brown spot under the microscope. While the round or polygonal 

 healthy cells of the pulp are regularly arranged and firm, those of the brown tissue are very irregular 

 in outline, and the starch-grains are enclosed within their walls. (Fig. 25.) They are collapsed 

 and broken down, the walls often lying flat against each other, and the starch-grains tucked in 

 between them. After a careful examination of numerous sections, from different varieties of 

 apples affected with Bitter Pit, I always found the discoloured tissue to consist of broken-down 

 cells, still retaining their starch-grains. There were also discoloured fibro-vascular bundles in the 

 vicinity, and more or less numerous cavities, as shown in Figs. 26 (a) and (b). When the pitted 

 apples were unripe, starch-grains occurred in the normal tissue as well as in the brown collapsed 

 cells. It is an important point to settle whether the dead cells have burst, owing to too great internal 

 pressure, or have collapsed from the failure of their water supply. 



It is not an easy matter to determine from a microscopic section, whether the cells have 

 burst or collapsed, since in the very act of making the section a certain amount of rupturing has 

 occurred, but their capacity for absorbing water will show whether it is a case of wilting or bursting. 

 The bursting of the individual cells from within is not likely, since each originally balloon-like cell 

 would be a buttress to its neighbour, and the whole would form a rigid body. However, a section 

 of a portion of a brown spot was made, and mounted at once, and photographed. (Fig. 28.) This 

 shows the collapsed cells, and large cavities scattered through the section. A section of the same 

 spot, in sequence, was made, and allowed to remain in water for 40 hours before photographing. 

 (Fig. 29.) The collapsed cells have evidently absorbed moisture and become distended, showing 

 that bursting had not taken place. This internal browning of the flesh of the apple may be brought 



