FUNGI IMPERFECTI 313 



which produced ; the former measure in extreme cases 50-150 x 

 4-5 fi, and the spores, 50-280 x 4-5 /*. They attain the maximum 

 size with both high humidity and temperature. The spores retain 

 their vitality for many months at least. Pure cultures of this fun- 

 gus may be readily secured by the poured plate method, and the 

 mycelium grows well upon bean stems and other media. In such 

 cultures the conidiophores are most peculiar. They may attain a 

 length of a millimeter (Fig. 145). Conidia may be produced and 

 abscised for a time, leaving the customary geniculation ; then 

 when the hyphse are longer, conidia-like branches arise, which re- 

 main attached, and eventually serve as true branches of perma- 

 nent hyphae. The mycelium, like that of the other Cercosporae, is 

 olivaceous ; but the colonies show minor peculiarities distinguish- 

 ing them from other species which have been thus cultivated. 



Control. This fungus may be controlled by early spraying with 

 Bordeaux mixture, 5-5—50 formula, or by repeated applications of 

 ammoniacal copper carbonate. It is also claimed that partial shade, 

 usually affording more equable temperature and moisture relations 

 for the host, enable the plant to resist the fungus to a very large 

 degree. 



XIX. LEAF BLIGHT OF COTTON 



Cercospora Gossypina Cke. 



Atkinson, Geo. F. Sphaerella Gossypina, n. sp. the Perfect Stage of Cerco- 

 spora Gossypina Cooke. Built Torrey Bot. Club. 18: 300-301. 1891. 



Atkinson, Geo. F. Cotton Leaf Blight. Ala. Agl. Exp. Sta. Built. 41 : 58- 

 61. fig. 19. 1892. 



Scribner, F. L. Cotton Leaf Blight. U. S. Dept. Agl. Rept. (1887): 355- 



357- pl- 4- 

 This fungus produces a leaf blight of cotton. It is more com- 

 mon on the less vigorous or old leaves, and it is generally reported 

 as prevalent when for any reason the vitality of the plant is lowered. 

 The spots are at first small and red, later becoming pale and finally 

 brown at the centers. They are generally 1-5 mm. in diameter, 

 but sometimes confluent and extensive. Conidiophores and conidia 

 are at first produced only in the central area of these spots, but on 

 leaves the vitality of which is largely lost the fungus may appear 

 over large areas. Atkinson considers this fungus a conidial stage 

 of Sphcerella Gossypina Atk. 



