Sept., 1916.] T. IIEMML—DIK-BACK DlSEASJ'J OF PAULOWNIA. 



307 



of the diseased 

 portion gradual- 

 ly dries up and 

 at last produces 

 numerous stroma- 

 ta of the fungus. 

 In the case of a 

 large tree, the pre- 

 sence of the fruit- 

 ing pustules of the 

 fungus may be 

 overlooked unless 

 careful observa- 

 tions l)e made, 

 owing to the 

 roughness of the 

 bark. Generally 

 the disease causes 

 defoliation one or 

 half month earlier 

 than in the case 

 of the health\' 

 tree. 





Morphology and Character of the Fungus. 



Mycelium. The hyphae are septate and branched, spreading 

 in the tissue of the bark and destroying the parenchyma cells. 

 They also penetrate deeply into the woody tissue, where the 

 hyphae are most commonh^ seen in the wood vessels and medul- 

 lar}- ray cells, although thev are also more or less present in 

 other portions of the wood. The color of the hyphae is almost 

 hyaline in the tissue of the host plant; but in most cultures the 

 mycelium becomes light flesh, light pink or yellowish brown in 

 color. The hyphae are not uniform in diameter, but vary from 

 0.8 to 6.0// (commonly 2.0-4.0/i). 



Stromata. In a 3'oung stage, a section through a pustule 



