228 MANUAL OF TREE DISEASES 



tinguished from one another except by the microscopic chap- 

 acters of the black fruiting-bodies which are just visible to the 

 unaided eye. The mycelium of both fungi causes powdery 

 white, more or less definite spots on the imder sides of the 

 leaves. The life histories and control of powdery mildew fungi 

 are discussed on page 37. 



Leaf-Bught 

 Caused by Glceosporium sp. 



This leaf-blight has been observed on Norway maple (Acer 

 platanoides) in Connecticut, New York and Virginia. No 

 studies have been made on the disease and but little is known 



Fig. 39. — Leaf-blight of maple caused by Glceosporium sp. 



concerning it. The leaves show yellowish and brown dead 

 areas along the main veins (Fig. 39). Later the leaves wilt 

 and fall from the tree. Minute brown spots form along the 

 veins. These are the fruiting-bodies (acervuli) of the causal 



