42 



BITTER PIT INVESTIGATION. 



colouring matter dissolved in the cell-sap originates, according to Pick (116), from tannin under the 

 influence of sunlight ; but since the red colour is sometimes all over the fruit, on the shady as well 

 as the sunny side, it cannot be altogether dependent on direct sunlight. 



The presence of tannin in this layer is made evident when sections are being cut with a razor. 

 In the freshly plucked or unripe apples, there is often a blue coloration produced, due to the action of 

 the iron on the tannin. And even the taste of the skin in many varieties indicates the large amount 

 of tannin present, for in pears particularly the skin has to be removed before they can be eaten 

 with pleasure. The relation of tannin and the production of starch in this region, to the development 

 of Bitter Pit, will be dealt with later. 



XV. — KESPLRATION OE THE APPLE. 



Plants are living things, and therefore they breathe just as animals, by taking in oxygen and 

 giving out carbon-dioxide gas, commonly called carbonic acid. Eespiration in the animal body is 

 a recognised sign of life, and the cessation of the process is regarded as a sign of death. In the 

 plant body there is not the same striking evidence, so that the breathing of plants or parts of plants 

 is not so generally known. But it is just as necessary for the plant as for the animal, since the products 

 of respiration are the same in both, viz., carbon dioxide gas and water, and it is the energy derived 

 from the oxidation of the various compounds during this process, that enables the plant to maintain 

 its vital activity. 



Living plants or parts of plants, however, can still continue to respire or give off carbon 

 dioxide gas, even when the supply of free oxygen is cut off. This is known as intramolecular respiration, 

 and, under such conditions, apples and pears, for instance, can still live for months. While the 

 apple is attached to its parent shoot, it may still be supplied with nourishment to make good the 

 loss due to respiration, but when it is picked from the tree, then it has to draw upon the materials 

 stored up within itself. Each living cell of the apple respires, and, when the fruit is placed in storage 

 there is a steady loss m weight, although it remains sound and firm. This is clearly shown by 

 Morse (113), who placed apples in cold storage in November, and weighed them at intervals of two 

 months : — 



Lose. 



January . . -33 per cent. 



March .. ..2-34 



May .. .. .. 3-60 



July ■• .. 4-71 



The reduction in weight is naturally thought to be due simply to the loss of water, but analysis 

 shows that the percentages of water and dry matter are practically constant, so that if solid matter 

 did not disappear as m the ordinary process of respiration, there would be a decreased proportion 

 of water and an increased proportion of dry matter. 



Morse has calculated the rate at which the apple changes its composition, at a summer 

 temperature and m cold storage, by an ingenious experiment, whereby the carbonic acid gas breathed 

 out of the apples was collected and measured. " It will be seen on comparing the average rates of 

 exhalation of carbonic acid at the different temperatures, that, in passing from meltin* ice (32° F ) 

 to cellar temperatures (45° to 50° F.), the rate nearly triples, and in passing from the medium 

 temperature to summer temperature the rate doubles." 



"Since the breathing out of carbonic acid is an indication of the rate of chemical change 

 within the fruit, it follows that changes of composition must take place from four to six times as 

 last at summer temperatures, as in cold storage, and from two to three times as fast in cool cellars 

 as m cold storage." 



