DISEASES OF WILD PLANTS. 97 



mm. in diameter on the lower surface and punctiform telia above. 

 Old or mature teliar generally show a gray center. 



Specimens collected : Austin, 24, 1421, 2884, 3113 ; San Antonio, 3160. 



INDIGO PLANT. 



Dodder (Cuscuta sp.). — The dodder was observed on the indigo 

 plant (Indigofera leptosepala Xutt.) in only a single locality. 

 Specimen collected: Boerne, 1639. 



KNOTWEED. 



Leaf -spot (Oercospora polygonacea Ell. and Ev.). — This disease on 

 the knotweed {Polygonum spp.) appears as subcuticular spots, 2 to 3 

 mm. in diameter, reddish brown above with a darker, raised margin 

 and a dark zone of tissue beyond the elevated border. Areas become 

 brown below and adjacent tissue becomes yellow. 



Specimen collected: Cuero, 2586. 



Powdery mildew (Erysiphe polygoni DC). — Both leaf surfaces 

 have a white, felty covering, due to the interlacing mycelium and the 

 summer spores. 



Specimens collected : San Marcos, 943 ; San Antonio, 1363, 3173 ; Austin, 3116. 



Rust {Puccinia polygoni-amphibii P.). — The minute reddish-brown 

 sori open to the under surface. Frequently they cause chlorosis and 

 death of the leaves. 



Specimen collected: San Marcos, 942. 



MALLOW. 



Leaf -spot (Oercospora malachrae Heald and Wolf, 32). — Circular or 

 subcircular spots are produced upon the leaves of the mallow (31a- 

 lachra capitata L.) . They are 1 to 4 mm. in diameter, with yellowish- 

 gray centers on which the conidial tufts are evident, surrounded by 

 a dark-purple border. The spots are slightly less pronounced upon 

 the under surface. 



The conidiophores are amphigenous, in fascicles of few to a dozen, 

 brown with slightly paler tips, nodose extremities, 90 to 120 by 4 to 

 5 fi, and several septate; conidia clavate, hyaline, slender pointed, 

 100 to 210 by 4 to 5 p, many septate. (PI. IV, fig. 3.) This species 

 of Cercospora seems to be distinct from the many described for dif- 

 ferent species of the Mallow family. It agrees most nearly with 

 C. polymorphs Bubak. 



Specimen collected: Victoria, 2347 (type specimen), 

 100833°— Bull. 226—12 7 



