Bitter Pit in Apples. 35: 



The colourless pulp, hoAvcvcr. after washing, gave black with 

 FeClj, and brown with sodium hydrate, showing tliat the tannic 

 acid had not been destroyed. Colourless acid pul]) dv colourless 

 boiled pulp turned brown on soaking in dilute sodium hydrate or 

 fiodum carbonate or ammonia, but remained practically colourless 

 after pounding up with precipitated chalk. 



If the pulp browned by alkali is immediately leplaced in acid 

 it becomes slowly colourless again, but if kept for some time the 

 brown colour is permanent, and is not removed In- acid. Colour- 

 less pulp just neutralised with sodium hydrate, ammonia or precipi- 

 tated chalk, darkens slightly on long exposure to air. but the 

 •colouration is feeble as compared with that produce<l in the presence 

 -of a slight excess of alkali. 



Causes of hroirii/ng. General ci>/icIi/k/ohs. 



The browning is due to the oxidation of tannic acid present in 

 numerous minute vacuoles in the protoplasm of the pulp cells, and "f 

 an iron-greening tannin present in the cell-sap. The former 

 appears to be gallotannic acid, and in the presence of free alkali its 

 oxidation is not necessarily dependent upon the presence of any 



•oxidase ferment. Oxidase action does not take place in acid media 

 beyond a certain strength. When the protoplasm dies slowly in air 

 the tannic acid in the presence of neutral or alkaline bases is 



■ oxidised. If killed rapidly by boiling, the oxidase enzyme is de- 

 stroyed, and the acid in the cell sap penetrates the protoplasm and 

 removes its alkalinity before the tannic acid has time to be oxidi.sed. . 

 On the addition of alkali, oxidation takes place. When the pulp is 

 killed by pounding or by pressure, brown oxidation products may 

 appear in the sap. Tannic acid and the brown oxidation products 

 combine rapidly with dying but uncoagulated protoplasm, and more 

 slowly with coagulated protoplasm. The broAvn colour imparted to 

 the protoplasm is then very permanent, and is not removed by acid. 



When living pulp cells are placed in poisonous solutiun.s 

 which destroy oxidases, the protoplasm i.s killed, and the tannic 

 .acid in the protoplasmic vacuoles is oxidised in the pre- 

 sence of its alkali or alkaline bases and of oxygen liefure 

 the vacuolar membrane loses its osmotic properties and allow.s the 

 acid of the sap to penetrate the protoplasm and remove its alka- 

 linity. If the poison used is a free acid aljove a certain concen- 

 tration, dependent upoTi its rate of diffusion, combining aviijitv 

 and ionisation, the alkalinity of the proToplasm is neutralised as it 

 "ir-5 killed, and no browning takes place. The tannic acid is, how- 



