EXUDATIONS AND ROTTING. 237 



peeling in shreds, the flesh more or less converted 

 into a putrid and stinking pulp, with a spotted 

 brown boundary of partly destroyed but firmer 

 tissue between the dark utterly rotten and the 

 white and still firm healthy flesh. The principal 

 agent in the destruction of the tissues is Clostridium^ 

 an anaerobic bacillus which consumes the cell-walls 

 but leaves the starch intact. Hence a thoroughly 

 decomposed tuber consists of a cork bag full of 

 starch and foetid liquid. In the dried condition 

 the flesh shows a brown marbling ; this passes into 

 a soft soupy starchy part, and here and there may 

 be violet grey cavities lined with Spicaria, 

 Hj'poinyces, etc., the white stromata of the latter 

 often appearing externally. The excavations are 

 filled with loose starch grains, and bounded by 

 cork and cambium formed in the peripheral cells. 

 The cell-walls eventually undergo slimy decom- 

 position. 



Spicaria, Fusisporiuni, various moulds, and 

 bacteria may all be associated with wet-rot. 



Dry-rot of Potatoes is also due to various 

 fungi and bacteria, but the destructive action goes 

 on slowly, owing to there being no more moisture 

 than the tissues afford. The flesh becomes ex- 

 cavated here and there, owing to the slow 

 destruction of the cell-walls by Clostridium : the 

 destroyed tissues are brown, and the uninjured 

 starch grains powder them all over. Finally the 

 whole shrunken mass has a crumbly consistency. 



When the flesh remains white, but assumes a 

 powdery consistency and dry-rot, with the cork 



