Bitter Pit (ind Sensitlc'dy to Polsonf^. 241 



kill the cell niifrlit inliihit the production of diastase, and there is 

 some evidence tu sliow that in certain plants (fungi, etc.), not only 

 poisons. l)ut also food substances may exercise a regulatory or 

 inhibitory action upoii the formation of diastase. Dr. White, 

 however, found diastase to be present at least in the early stages 

 of bittei- pit. As it is not possilile to detect metallic poisons in 

 bitter pit tissue l)y the diastase mctlidd. what is needed is a com- 

 plete exhaustive percentage analysis of the ash of bitter pit tissue, 

 using large (piantities of material, and iiit'thods of concentration 

 like those which enable traces of certain metals to be extracted 

 from their ores. No such analyses have as yet been made, and 

 they lie more in the province of the chemist than of the plant 

 physiologist, but the significant fact noted by Mr. P. R. Scott, that 

 the percentage of ash is higher in bitter pit tissue than in normal 

 pulp, merits further investigation. 



Summary. 



In all cases potatoes are less sensitive to i)oisons than apples, 

 the differences in the resistance varying from 1000 times ('anaes- 

 thetic), to 8 or 10 times (alkali and copper sulphate). Mercuric 

 chloride and copper sulphate are about e<|ually poisonous to pota- 

 toes, and sulphuric acid is only slightly less pf)isonous than lead 

 nitrate, and is some 50 times as poisonous as is alkali. 



As in the case of apples, the sensitivity to poisons is much 

 greater at high than at low temperatures. Tannic acid precipitates 

 starch from its solution in water. The precipitate dissolves on 

 boiling, and forms again on cooling, even in the presence of hydro- 

 chloric acid. The precipitate can be obtained in gluten-like masses 

 soluble with difficulty, or imperfectly soluble in diastase, and in 

 hot water, but readily soluble in dilute hydrochloric acid on boil- 

 ing. The occasional resistant starch grains found in apples have 

 possibly been in contact with the tannic acid of the cell-sap. They 

 will dissolve in diastase after warming with dilute hydrochloric 

 acid, and then washing well. 



The presence of 0.0003 to 0.003 per cent, of tannic acid distinctly 

 retards diastatic action; 0.003 to 0.06 per cent, strongly retards 

 it, and 0.33 to 1 per cent, practically inhibits it. This effect is 

 shown at 35° C, and is still more pronounced below 20c> C. The 

 cell-sap of apples may contain up to as much as 0.1 per cent, tannic 

 acid, and bitter pit tissue appears to contain more than normal 

 pulp. This will protect any starch grains extruded into the cell- 



