1905.] 



Potato Leaf-Curl. 



477 



again produces the disease in the haulm and leaves. This, how- 

 ever, is not the only source of the disease, as experiments have 

 shown that the young " sprouts " are readily infected with the 

 spores of the fungus, and from this point of infection the 

 mycelium extends up the haulm. 



Potato Leaf-Curl. 



Neither the leaves nor the haulm above ground can be infected 

 by the spores of the fungus. This limits the appearance of the 

 disease to two causes: — (1) To the presence of mycelium in 

 the tuber ; by this method, new and hitherto clean areas become 



