296 DISEASES OF ECONOMIC PLANTS 



the disease, but the outlay might not be warranted except 

 in special instances. 



White rust (Albugo ipomaece-pandurancB (Schwein.) 

 Swingle). — White, glistening sori, 1 mm. or so in diameter, 

 appear upon the undersides of the leaves, and upon 

 the stems. These rupture and set loose a mass of powdery, 

 snow-white spores. The tissue surrounding the sorus is 

 pale, or yellow, as seen from the opposite side of the leaf. 

 The tissue surrounding old sori dies, and brown patches 

 result. 



No large injury usually comes from the disease. 



TOBACCO 



Root rot (Thielavia basicola (B. & Br.) Zopf.). — Known 

 in Europe since 1897, thielaviose was first reported in 

 the United States in 1904, as occurring upon tobacco, 

 though it has probably been long prevalent in tobacco 

 sections. It has been noted upon other hosts: namely, 

 violets in Connecticut, Maryland, and District of Columbia ; 

 ginseng in Ohio and New York; also upon begonia, catalpa, 

 and clover. Upon tobacco it is now known in Ohio, Con- 

 necticut, Kentucky, and North Carolina, and its territory is 

 increasing yearly. 



Thielaviose in the seed bed often causes the entire crop 

 of seedlings to be discarded, delaying planting or compelling 

 a change of crop. In the field the loss sometimes amounts 

 to 25 per cent. 



The disease is recognized by the black decay upon the 

 roots, sometimes a cracking and deformation on the stem 

 just above the roots, and the failure of the plant to develop 

 normally. 



