SHADE TREES. 



195 



Schw.) grows in the secretions of woolly aphis, causing a large spongy black mass 

 on the leaves. 



Hawthorne {Cratwyus).- — -The leaves of the English hawthorne are affected 

 often seriously with Entomosporium thumenii Cke., which produces spots. 



Ash (Fraxinus). — The stems and leaves of the ash for the past few years have 

 been troubled with a rust (^cidium fraxini Schw.). The worst cases have been 



Fig. 67. — Linden leaf spot {Cercospora). 



found in the vicinity of Cape Cod. The ash is also .subject to a leaf spot (Septoria 

 leucostroma E. & E.) and mildews (Phylluctinia suffulta (Reb.) Sacc. and Phyl- 

 losticta viridis E. & K.). 



Locu.ST (Robinia). — The locust is unusually susceptible to borers, and when 

 attacked by them often becomes infected with various species of fungi. 



Linden (Tilia). — The leaves of the linden are sometimes badly affected with 

 leaf spots, such as Ccrcospora microsorn Sacc, which may be largely controlled by 



Fig. 68.- 



Linden tree in center sprayed twice with Bordeaux riiix- 

 ture; others unsprayed. 



spraying. The linden, in some locations suffers verj- badly from frost cracks. The 

 American basswood (Tilia americana) is subject to a leaf mildew {Uncinula clin- 

 tonii Lev.) and to the leaf spot {CercosjMra tilia Pk.). 



Elm {Ulrmis). — The most common leaf spot found on the elm is Dothidella ulmi 

 (Duv.), which is characterized by numerous small black spots on the upper surface 

 of the leaves. Another leaf spot caused by Phleospora ulmi Wallr. is characterized 

 by numerous small spots from which gelatinous masses exude in damp weather. 



