2IO FUNGOUS DISEASES OF PLANTS 



very few species. Some are parasitic and some saprophytic, 

 some with superficial mycelium, and others with mycelium pene- 

 trating the substratum. Two genera which are important in this 

 connection are Thielavia and Meliola. In the former genus the 

 Mycelium is immersed in the host. The perithecia are mem- 

 branous, without appendages, and subsidiary fruit forms include a 

 stage with endogenous spores. In the genus Meliola, the mycelium 

 is superficial and brown. The perithecia are beset with simple 01 

 branched appendages. The spores are brown and two-celled. 



XIX. ROOT ROT OF TOBACCO, VIOLETS, PEAS, LUPINES, ETC. 

 Thielavia basicola (B. & Br.) Zopf. 



Briggs, L. J. The Field Treatment of Tobacco Root-Rot. Bur. Plant Ind., 



U. S. Dept. Agl. Circular 7 : 1-8. 1908. 

 Clinton, G. P. Root Rot of Tobacco. Conn. Agl. Exp. Sta. Rept. (1906): 



342-368. pis. 29-32. 

 Thaxter, Roland. Fungus in Violet Roots. Conn. Agl. Exp. Sta. Rept. 



(1891): 166-167. 

 Zopf, W. Ueber die Wurzelbraune der Lupinen, eine neue Pilzkrankheit. 



Zeitsch. f. Pflanzenkr. 1: 72-76. Jigs. 1,2. 1891. 



This fungus, which is now known to cause in the United 

 States, under certain climatic and soil conditions, a serious 

 disease of tobacco {Nicotiana Tabacum), was first studied in 

 Europe as a parasite of less consequence upon peas, lupines, etc. 

 The morphology of the fungus and its relation to a disease of 

 Senecio elegans was established in 1876. The fungus was found 

 in the United States on violets {Viola odorata) in 1891, and sub- 

 sequently on other plants ; but in 1906 it was recognized in 

 Connecticut as an important tobacco parasite. 



Distribution. Upon one or more of its hosts the fungus has 

 been found, in general, from Ohio eastward in the United States, 

 and in western Europe from England to Italy. The fungus has 

 not been reported from the southern states growing tobacco, 

 or from tropical regions. It is believed that abundant moisture 

 is essential for serious trouble by this fungus, lack of drainage 

 and other factors assisting in producing this condition. Briggs 

 has recently shown that the presence of this fungus in tobacco 

 soils is an indication of alkalinity, a condition often brought 

 about by the system of fertilization. 



