SYCAMORE OR PLANE-TREE DISEASES 



335 



late frost-injury (see page 21). The usual type of lesions, how- 

 ever, develops later, as elongate independent brown spots along 

 the main veins of the leaf. The diseased condition of the vein 

 and adjoining tissues, causes the rapid death of the leaf-tissue 

 around the original 

 spot, resulting in 

 larger dead brown 

 areas (Fig. 66). 

 Two or more such 

 lesions finally in- 

 volve the entire leaf, 

 and the tree, when 

 infection has been 

 general, appears 

 from a distance as if 

 scorched. In moist 

 weather, small pin- 

 head-like, cream- 

 colored spots are 

 produced on the 

 under sides of the 

 leaf along the veins 

 which are included 

 in the dead areas. 

 The leaves' soon 

 drop after being 

 killed and often the 

 tree is completely 

 defoliated and re- 



FiQ. 67.- 



- Sycamore defoliated by leaf-blight 

 fungus. 



mains bare until later in the summer, when new leaves are 

 developed (Fig. 67). 



The smaller twigs are also killed and cankers are formed on 

 the branches of an inch or less in diameter, sometimes girdling 

 them (Fig. 68). At first, the cankered area is sunken with a 



