66 A PLANT-DISEASE SURVEY 1ST TEXAS. 



Leaf -scab (Gnomonia ulmea (Sacc.) Thm.). — Elm leaves affected 

 with this fungus show minute spots scattered over the surface. 

 These spots, which are 1 to 3 mm. in diameter, show on the upper 

 surface a central cluster of small black pustules surrounded by a 

 border of dead tissue, white or gray in color; or the black pus- 

 tules may be somewhat concentrically arranged. In the early stages 

 of development the spot will not be noticeable on the under surface, 

 but in the later development the under surface shows a definite 

 brown area of dead tissue opposed to the white zone of the upper 

 surface. In this stage the epidermis of the under surface is ele- 

 vated in numerous pustules and ruptured to some extent by the 

 protruding beaks of the perithecia. The late fall collections show 

 only immature perithecia. The white zone bordering the perithecial 

 pustules is caused by the accumulation of large quantities of crystals 

 in the epidermal cells (PI. XIII, fig. 1). 



In many of the collections, especially upon the late collections of 

 Ulmus alata, a Coniothyrium is present. The pycniclia of this fun- 

 gus may be present on either surface of the spots and produce an 

 abundance of oval, brown spores 3.5 to 4 by 6 jx. It is possible that 

 this represents a pycnidial stage of the Gnomonia, but proof of a 

 definite connection must be obtained by cultures. It may be noted in 

 this connection that a Phoma-like pycnidium has been observed in 

 connection with Phomatospora (25), a genus belonging to the 

 Gnomoniaceae. 



Some specimens of Ulmus alata show a third type of fruit. These 

 fruits show as minute erumpent papillae scattered abundantly over 

 the under surface, while the upper surface shows a marked yellow 

 punctate appearance. The spores produced are two to three septate, 

 21 to 39 by 4 /a, and hyaline. These spores may be the only form 

 present on the leaves at a given time, or they may be found in con- 

 nection with the perithecial stage of Gnomonia. These spores and 

 pycnidia show a marked similarity to Phleospora ulmi (Fr.) Wallr. 

 (36), and it seems probable that they represent a stage in the life 

 history of our Gnomonia, since Klebahn (36) has proved a similar 

 connection between Phleospora ulmi (Fr.) Wallr. and Mycosphaerella 

 ulmi) another genus of the Sphseriales. 



Specimens collected: (1) Ulmus alata Micnx. — Austin, 255, 256, 338; Llano, 

 1749. (2) Ulmus crassifolia Nutt. — New Braunfels, 1675; Uvalde, 1928; Seguin, 

 2312; Elgin, 1874. (3) Ulmus americana L.— Round Rock, 2419. 



Leaf -spot (Cylindrosporium tenuisporum Heald and Wolf, 32). — 

 The small-leaved elm is affected by a leaf-spot which shows as brown 

 circular or slightly irregular areas, 2 to 10 mm. in diameter, generally 

 with a gray center and a narrow yellow border. The under surfaces 

 of the spots are more uniformly brown and show minute black specks, 



226 



