33 



stem. When the disease has not entirely destroyed the tissues of the stem 

 the sap may ascend to the leaves where plant food is manufactured as in 

 the normal plant, but the return current is prevented from passing down 

 beyond the dead blackened area. As a result, small tubers form above the 

 injury (Fig. 1). 



It is an easy task to pick out in a field the potato plants that are 

 diseased. Such plants have not the bright green colour of the unaffected 

 healthy plants and are not so thrifty and strong. In severe cases of attack 

 the fungus has the habit of a daraping-off disease. 



Some observers are of the opinion that this fungus is not responsible 

 for the production of the little potatoe.'i that form above the injured area, 

 but, so far as could be ascertained, during the past season no other fungus 

 was present (Fig. 2). 



Fig. 2 — Rhizoctonia disease of Potatoes. Photograph showing the blacic dead areas on the stems and the formation of 

 tubes above the afTected area. 



I. P.— 3 



