Trees and Tirnber 405 



excess of soil moisture; Sun-bum of nuts or tree trunk; 

 Crown-gall; Perforation, an imperfection in shell develop- 

 ment; Root-rot; Wilt; Yellows; and Leaf-spot (Marssonina). 



WILLOW 



Rust (Melampsora saltciscaprce (Pers.) Wint.). — Of tree 

 rusts this is one of the most prevalent, occurring as dusty, 

 yellow sori upon the lower leaf surfaces. Trees are rendered 

 unsightly by the defoliation induced. In the latter part of 

 the season the winter sori appear as reddish brown to black, 

 waxy or crusty spots. A similar rust is conmion upon cotton- 

 wood, Balm of Gilead, poplar. Canker (Cytospora).—See 

 poplar. 



