AUTOBASIDIOMYCETES 479 



of the clover diseases and frequently becomes epidemic in planta- 

 tions of alfalfa, or lucern, a highly important forage plant of 

 Central Europe. In asparagus growing the losses are also occa- 

 sionally severe. 



An ascomycetous fungus occurring upon the stubble of alfalfa, 

 described as Leptosphceria circinans Fckl., has been by some re- 

 garded as the perfect stage of Rhizoctonia Medicaginis, yet 

 through cultures of ascospores the writer has been unable to pro- 

 duce a mycelium resembling that of the Rhizoctonia. Moreover, 

 the mycelium of the Rhizoctonia has been unusually difficult to 

 propagate in artificial cultures. 



XV. ROOT ROT OF COTTON AND ALFALFA 

 Ozonium omnivorum Shear 



ATKINSON, GEO. F. Method for Obtaining Pure Cultures of Pammel's Fun- 

 gus of Texas Root Rot of Cotton. Bot. Gaz. 18 : 16-19. l &93- 



PAMMEL, L. H. Cotton Root Rot. Texas Agl. Exp. Sta. Rept. 2: 61-86. 

 1889. (Also published as Built. 7: 1-30. 1889.) 



SHEAR, C. L., and MILES, G. F. The Control of Texas Root Rot of Cotton. 

 Bur. Plant Ind., U. S. Dept. Agl. Built. 102 (Pt. 5): 39-42. 1907. 



In Texas and other neighboring states a serious root rot of cot- 

 ton (Gossypium spp.) and alfalfa (Medicago sativa) has been known 

 for a number of years. It is not, however, confined to these hosts, 

 and among cultivated plants the sweet potato (Ipomcea Batatas] is 

 also affected. Pammel in 1 889 reported it on ten or more deciduous 

 trees and also on a few herbaceous weeds. During the summer of 

 1901 I found this fungus on twelve different weeds in a single 

 cotton field near Paris, Texas. Since these hosts represent a 

 number of widely separated orders, it is apparent that the fungus 

 is practically unrestricted. It does not, however, seem to occur 

 upon monocotyledonous plants. 



Little is known about infection and the progressive stages of 

 the disease. There is apparently very little evidence of the trouble 

 until the plant suddenly wilts and dries up. It would seem that 

 cotton plants are far more commonly killed after some of the bolls 

 begin to mature. Certainly dead stalks become more evident from 

 this time forward. Nevertheless, plants have been killed by the 

 fungus before even any definite flower buds, or squares, have 



