106 TREE WOUNDS AND DISEASES 



and are inky black, which is well set off by 

 the margin of dirty yellow. 



The attacked portion of the leaf becomes 

 wrinkled and much thickened in texture, 

 while all the affected foliage drops off pre- 

 maturely. After lying on the ground during 

 the winter, the thread-like spores are emitted 

 in vast quantities at the time when the foliage 

 of the sycamore is appearing in May and 

 June. It is, however, not only the sycamore 

 that is attacked by this fungus, for the Norway 

 maple and our native field maple (Acer cam- 

 pestre) are equally liable to injury, and have in 

 some instances suffered very severely. 



Altogether this fungus is a formidable pest, 

 that is becoming yearly more plentiful and 

 disfiguring the maple and sycamore leaves to 

 a wide extent. Another fungus which infests 

 the leaves of these trees is Rhytisma punctata^ 

 which may at once be distinguished from the 

 former species by the many small black spots 

 studded thickly together, which combine to 

 form the large conspicuous blotches for which 

 affected trees are remarkable. Both species 

 are sometimes found on the same leaf. As 



