Bitter Pit in Apples. 21 



membrane has, so that a dissolvtMl sul)stance which is not poisonous 

 inside the cell is not poisonous outside it. This is the more sur- 

 prising because some of the cell contents when applied in pure form, 

 are capable of exercising a poisonous action. Possil)ly this may be 

 i\ question of ionization, of combination or of relative influence 

 on the surface tension of the ectoplasmic membrane, and hence oil 

 diosmosis. The acidity of the sap of the ripe Yates' Pippin apples 

 used was such that 2^ litres were equivalent to 10.6 grams of normal 

 sodium carbonate. This is witliin the limit of dilution for the 

 poisonous action of malic, citric and oxalic acids when used in 

 pure form, and with exposures of a week's duration. It has already 

 been shown that the poisonous action of a mixture of substances 

 may be much less than when each is applied singly, and apparently 

 it is this fact which explains partly at least, the practically non- 

 poisonous character of freshly extracted apple sap to pulp cells when 

 applied externally. 



Alkali. — Since the protoplasm of the pulp cells is alkaline, 

 although the sap is acid, the vacuolar membrane must be able to 

 prevent the acid in the sap from entering the protoplasm, and we 

 should expect to find the protoplasm more resistant to alkalis pene- 

 trating from outside than to acid. This has already been shown to 

 be the case with ammonia and Jonathan apples, and it applies still 

 more with caustic potash and the more resistant Yates' Pippin. 



CAUSTIC POTASH. PREPAKED YATES PIPPIN IMMERSED FOR 

 5 DAYS AT 3-1 8X\ 



Strength of Solution. Result. 



5 grams per 1000 c.c. - Dark brown pits to each prepared spot, 1-2 mm. 



diameter and depth. 



1 gram per 1000 c.c. - Faint superficial browning to no signs of poisoning. 



1 gram per 10,000 c.c. - No distinct signs of poisoning. 



1 gram per 100,000 c.c. - No signs of poisoning. 



With dilute solutions, however, the CO^ produced by the respiring 

 pulp cells would suffice to turn the diffusing KHO molecules into 

 potassium carbonate, so that the alkaline action of caustic potash 

 would be less evident than with equal dilutions of ammonia. In 

 fact, with a 1 per 1000 dilution, the poisonous action may be largely 

 due to the potassium ions, rather than to the hydroxyl ions. 



Alcohol. — During the anaerobic respiration of apples small quan- 

 tities of alcohol are produced, and are apparently to some extent 

 transferred from the protoplasm Avhich forms them into the cell 



