SHADE TREES. 



195 



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

 on the leaves. 



HAWTHORNE (Cratcegus) . The leaves of the English hawthorne are affected 

 often seriously with Entomoxporiinn thumcnii Cke., which produces spots. 



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

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



Fi<;. 07. Linden leaf spot (Cercoaporn). 



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

 Ifucostroma E. & E.) and mildews (Phyllactinia suffulta (Reb.) Sacc. and Phyl- 

 losticta viridis E. & K.). 



LOCUST (Robinia). The locust is unusually susceptible to borers, and when 

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



LIX~DEX" (Tilia). The leaves of the linden are sometimes badly affected with 

 leaf spots, such as Cercospora nticrotora Saee., which may be largely controlled by 



FIG. 68. Linden tree in center sprayed twice with Bordeaux mix- 

 tare; others unsprayed. 



spraying. The linden in some Locations suffers very badly from frost cracks. The 

 American basswood (Tilio <nm rlcand) is subject to a leaf mildew (Uncinnln din- 

 tonii Lev.) and to the leaf spot (Cercospora tilia Pk.). 



ELM (Ulnnis). 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. 



