Alabama College Station, Bulletin No. 27 (New Series), May, 1891 (pp. 16). 



Elack kust of cotton, G. F. Atkins* »n, Vn. 1>. (i>liit('s \i). — 

 This is, iu substance, a paper read before the section on botany of the 

 Association of American A<;ricultural Collejies and I'^xperinient ^Sta- 

 tions, in November, 1S!)0, and afterwards published in tlie Jiotanical 

 (lazetle, vol. xvi (1891), pp. (51-05. The author calls attention to the 

 confusion existinj:^ with reference to the name of this disease, which is 

 not a true rust. Jlis observations indicate that what is popularly 

 known as " black rust of cotton " is of a complex character. " The 

 fungi commonly present and which play an important p:irt in the dis- 

 ease, are Cercosvora (jossypina, Cooke, CoUetotrichuvi (/onsypii, E. A. 

 Southworth, Macrosporium nigricantium, Atkinson, a si)ecies of Alter- 

 naria, and a bacterial organism which sometimes produces a charac- 

 teristic disease of the leaves." The ditlcrence between leaf blight and 

 black rust of cotton is pointed out, and the botanical characters of the 

 fungi connected with the latter disease are described and illustrated. 

 The author has observed on dead leaves of cotton a spha liaceous fun- 

 gus which he thinks is probably the ascospore stage of Cefconpora 

 gossypina. The following is taken from his descri[)tion of }facrosporium 

 nigrkaniium (see also Botanical Gazette, vol. (xvi 1891), p. 62): 



The hyph.-o are dark or olive browu and borne on both sides of the leaf. At the 

 enhirgenients there is usually a darker band around the center. The hypha' thus have 

 a nodulose appearance, as in such species as J/«c)-osj<orii<m paj-asi/icHni, Thiini. The 

 spores are olive browu, oblong, constricted in the middle, and stoutly rostrate at one 

 side of the apex. As the young spore develops it is constricted in the middle before 

 the first transverse i)artition is formed. This is formed iu the constricted portion. 

 Later other transverse, longitudinal, and obli(iue septa are produced. * ' * fhe 

 fertile hy]>h;« are usually scattered, rarely in clusters of two or three. Measure- 

 ments: Hyphai are 0.050 toO.140"'"' long by O.OOG to 0.007'"'" in diameter; conidia, 

 0.018 to 0.02'2""" by 0.03G to 0.050""". 



The Alternaria is illustrated from a water culture under the micro- 

 scope. The fertile hypha' produce concatenate spores. Both the spores 

 and the fertile hypha' are dark brown in color and when occurring in 

 considerable numbers blacken the leaf. 



The bacterial disease is often very widespread, even when no evidences of the other 

 fungi are to be found, but is mentioned here because frefjuently it is an accompani- 

 ment of the black "rust" and contributes materially to the aggravation of the dis- 

 ease. It is first manifested by a watery ai)pearance in delinite areolate spots, which 

 are bounded by the veinlets of the leaf. The spots are sometimes very numerous and 

 fro<iuently conjoined; often the disease follows one or more of the main ribs of the 

 leaf, being bounded on each side by an irregularly zigzag line. As the disea.se ages, 

 the spots become blackish and theu light brown, then fre<iuently bordereil by a black- 

 ish color where the disease has extended somewhat centrifugally. The der.d .sjiots iu 

 the leaves sometimes break out, leaving many perforations in the leaves with ragged 

 edges, somewhat as results in cotton leaf blight. The disease hastens the falling ott" 

 of the leaves. 



Extanal characters and jirof/ress of the disease. — During the entire season (from .Inly 

 to the close of October), of the thousands of leaves, old and young, that I examined, 



