DISEASES OF TREES AND SHRUBS. 59 



Each spot shows one and occasionally two acervuli, which occupy 

 the middle of the light-brown, central area. A straight or curved 

 mass of spores may be seen extruded from the acervulus, which is im- 

 mersed in the tissue of the under surface. The spores are 45 to 60 

 by 3 to 4 /x, 3 to 6 septate, generally slightly curved, nearly cylin- 

 drical but sometimes tapering, and hyaline. (PL VI, fig. 4.) 



The disease was observed during the season of 1908 in a much more 

 severe form than in 1909. In all cases it was observed only on 

 nursery trees which were badly crowded. 



Specimens collected: Austin, 459, 1909 (type specimens) ; Georgetown, 2354. 



Root-rot (Ozonium omnivorum Shear). — This disease was found in 

 a nursery where it had destroyed a small group of young trees (5 or 

 6 years old). The disease had spread across all of the rows and 

 when observed was advancing along the rows. Roots removed from 

 the soil showed the characteristic yellowish-brown filaments. 



Specimen collected: Georgetown, 2351. 



BOX. 



Leaf -blight {Macrophoma candollei (B. and Br.) Berl. and 

 Vogl.). — The leaves of box (Buxus sempervirens L.) become entirely 

 dry, with scattered black pycnidia 250 to 300 n in diameter on both 

 surfaces. The conidia are 36 to 40 by 10 to 11.5 p, hyaline, and 

 densely granular. 



Specimens collected : New Braunfels, 1666 ; Georgetown, 2357. 



BOX ELDER. 



Leaf -spot (Gloeosporinm negundinis Ell. and Ev.). — As a result of 

 the attack of this fungus on box elder {Acer negundo californicum 

 (T. and G.) Sarg.), circular or subcircular straw-colored spots 3 to 5 

 mm. in diameter are formed. Most commonly they are so abundant 

 as to result in the formation of larger dead areas, due to the fusion 

 of spots. The yellow color is more pronounced on the under surface. 



The acervuli are 125 to 200 p in diameter, brown or blackish, and 

 more abundant on the upper surface. The spores are oval, guttulate, 

 and 15 to 20 by 5 to 7 fi. G. negundinis Ell. and Ev. on the twigs of 

 the box elder, as determined from measurements of spores from 

 specimens in the mycological herbarium of the Bureau of Plant 

 Industry, shows a range of spore size from 5.9 to 6.6 by 16.5 to 19 /x. 



Specimen collected: Lockhart, 2060. 



Leaf tip-blight (Septoria marginata Heald and Wolf, 32). — The 

 tips and margins of the leaves are killed, the dead areas being brick 

 red, light brown to straw colored, or nearly gray in some cases, and 

 confined to a narrow zone at the leaf tip or margin, or extending 



228 



