34 



The disease winters over on the surface of tubers as black spots called 

 Sclerotia. These become very evident when affected tubers are washed 

 under running water. On examination, the sclerotia are seen to be com- 

 posed of dense masses of mycelium with threads of a characteristic shape. 

 The threads are much branched, often irregularly ; often breaking off into 

 short lengths of one cell or more ; the cells are short and are much con- 

 stricted at the ends (Figs. 3 and 4). 



^^* 



Fig. 3 — Tuber of Potato spotted with black Sclerotia of Rhizoctonia. 



Fig. 4 — The large, closely septate hyphae which make up the short tufted growth of Sclerotia. 



