Nov. 29. 1915 Varietal Resistance of Plums to Brown-Rot 385 



was still firm in the center. After 48 hours it had softened completely. 

 A portion not immersed in the liquid, but which came in contact with it 

 at one point, was softening from this point and becoming discolored. 

 The checks in water remained firm and were not discolored. 



Although the effect of the extract on the apple tissue appeared to be 

 that of a pectinase, it can hardly be concluded that this enzym was 

 present, as the fruit used was overripe and slightly mealy, and could very 

 easily have been broken down by other solvents contained in the extract. 



DeBary (1886) considered the possibility of oxalic acid being the toxic 

 substance produced by 5. lihertiana, because he found the hyphae often 

 coated with crystals of it; however, he later discarded this notion for 

 the reason that solutions of oxalic acid did not give the same effect as the 

 fungus. Smith (1902) extracted a substance from Botryiis cinerea, 

 which, whether boiled or unboiled, caused a rot of the host tissue iden- 

 tical with that caused by the fungus. He concluded it was not an 

 enzym, but that the effect might be due to oxalic acid, which he found to 

 be present in quantities often as high as 2 per cent. Peltier (191 2) con- 

 firmed the results regarding this action of the extract, but was unable to 

 detect the presence of oxalic acid, even in old cultures. 



The possibility of oxalic acid being the toxic substance of S. cinerea 

 was considered, as Cooley has demonstrated that it is produced in appre- 

 ciable amounts in cultures of 5. cinerea on plum and peach juice, and 

 in peaches which had been rotted by the fungus. In order to determine 

 the effect of oxalic acid on vegetable tissue, small blocks of onion, potato, 

 tomato, dahlia, radish, coleus (young shoot), tomatoes (young shoot), 

 loquat (fruit), canna (bulb), oxalis (petiole), geranium (young shoot), 

 and apple were immersed in 0.015, 0.062, 0.125 per cent solutions of 

 oxalic acid and the effect noted at the end of 24 and 48 hours. In all of 

 the solutions the apple, loquat, and oxaHs softened, while in the 0.125 

 per cent solution only the onion and tomato softened slightly. The 

 potato did not soften even in 0.25 per cent solution. In all cases bleach- 

 ing occurred. An examination of the different tissues showed that the 

 softening was due to the solution of the middle lamella. 



The fact that oxalic acid even in such dilute solutions readily softened 

 the tissues of the apple and loquat, upon both of which the brown-rot 

 grows readily, might indicate that the oxalic acid was the toxic sub- 

 stance, but the bleaching effect produced by the acid and the fact that 

 when used even as strong as 0.25 per cent it had no effect on potato, upon 

 which the fungus also grows readily, would seem to indicate that this acid 

 is not the sole toxic substance produced. 



COMPARISON OF FIRM-ROT AND SOFT-ROT 



Cooley (191 4) pointed out the very interesting fact that, although 

 P. expansum and 5. cinerea apparently acted differently on their hosts, 

 the one producing a soft-rot of fruits and the other a firm- rot , in culture 



