MOULDS. 149 



parts beneath. The whole soon dries up^ and ia 

 many instances exhibits in the centre the black, 

 irregular fungoid masses which are known under 

 the name of Sclerotium vamum, and which are 

 believed to be the mycelium of certain moulds in 

 a high state of condensation. 



^^ If the tubers are now examined, the greater part 

 will often be found smaller than usual, especiallly 

 if the disease has commenced at an early stage of 

 growth ; but in their natural condition, while here 

 and there a tuber, particularly if it has been 

 partially exposed, exhibits traces of disease. The 

 surface is, however, soon marked with livid patches, 

 commencing generally about the eyes, or at the 

 point of connection with the fructifying shoots : 

 these rapidly acquire a spotted appearance, the 

 spots being rather waved, and assuming often a 

 more or less concentric arrangement. Sometimes — 

 especially on the smoother kinds of tuber — two or 

 more regular systems of concentric spots are exhi- 

 bited on the same tuber. The skin now withers, 

 and is easily separated ; the spots become depressed 

 and of a yellowish tinge ; and if the tubers be laid 

 in a moist place, in a day or two — sometimes in a 

 few hours — the same mould which destroyed the 

 leaves springs from them, piercing the cuticle from 

 within, yet not scattered, as on the leaves, but 

 forming a conspicuous white tuft. If a section of 

 the diseased tuber be made on the first symptoms 

 of the disease, httle brownish or rusty specks are 



