DISEASES OF WILD PLAXTS. 95 



lar spots, 2 to 5 mm. in diameter, brown or grayish in color, with a 

 slightly darker border, frequently surrounded by a zone of yellow. 

 Sometimes the spots become confluent, causing the death of the leaves. 



Specimens collected: Austin, 1558; Seguin, 2324; Georgetown, 2378. 



Rust (C oleosporium vernoniae B. and C). — Minute yellow pustules 

 are very abundant on the lower surface of the leaves and cause a 

 yellow, punctate appearance of the upper surface. 



Specimen collected : Austin, 345. 



FLEABANE. 



Leaf-spot (Septoria erigerontea Pk.). — This disease on the fleabane 

 (Erigeron canadensis L.) appears as distinct spots, 1 to 2 mm. in 

 diameter, with a grayish center and brown border on the leaves, most 

 abundantly on the lowermost. The black pycnidia show very plainly 

 in the grayish center. The spores are 24 to 78 ^ in length, which is in 

 excess of the original description (39). 



Specimen collected : Austin, 3033. 



GAURA. 



Rust (Uromyces gaurinus (Pk.) Long.). — The cluster cups on 

 gaura (Gaura coccinea Pursh.) appear on both surfaces of the leaves 

 and are so numerous that the leaves are destroyed. 



Specimens collected : Austin, 2945, 3000. 



GIANT RAGWEED. 



Dodder {Cuscuta indecora (?) Choisy). — Found in only a single 

 locality, where it was growing abundantly on the giant ragweed 

 (Ambrosia trifida L.), as well as several other hosts. 



Specimen collected : San Antonio, 1777. 



Powdery mildew (Erysiphe cichoracearum DC). — The collections 

 of this fungus include only conidiospore specimens. 



Specimens collected : San Marcos, 949 ; San Antonio, 3155. 



Rust (Puccinia xanthi S. var. ambrosiae B. and Rav.). — This 

 variety is quite similar to the rust on the cocklebur, but the sori are 

 more abundant and generally smaller. 



Specimen collected : Austin, 1415. 



GOLDENROD. 



Leaf-spot (Cercosporella reticulata Pk.). — Numerous brown spots 

 with indefinite margins appear on the leaves of the goldenrod (Soli- 

 dago spp.). The spots are often confluent and the leaf tips may be- 

 come brown, the tissue adjacent to the areas being killed. 



Specimen collected: Elgin, 2007. 

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