CHAPTER VI. 



SMUT OP POTATOES. 



Tubercinia scabies, B. 



THE smut which produces one form of scab in potatoes 

 is caused by an olive-green or brownish fungus, of sub- 

 terranean habit, named Tubercinia scabies, B. ; from tuber, 

 an ancient Roman name for a fungus ; cineres, ashes ; and 

 scabies, the itch. This is the same with Bhizosporium 

 Solani, Rab., and is the Protomyces of Martius. The smut 

 fungus, which is very common upon potatoes, is supposed 

 to be allied to the bunt of wheat, Tilletia caries, Tul. ; and 

 the smut of corn, Ustilago carlo, Tul. It was described 

 and illustrated by Martius, Die Kartoffel-Epidemie, p. 23, 

 tab. 2, Figs. 9-13, tab. 3, Figs. 36-38, and afterwards by 

 the Rev. M. J. Berkeley in the Journal of the Royal 

 Horticultural Society, vol. i., 1846, page 33, Figs. 30 and 

 31 . The spores are compound, and are composed of minute 

 cells, which together form a hollow globe with one or more 

 apertures. In this character Tubercinia agrees well with 

 the allied genus Urocystis (formerly Polycystis, in reference 

 to the spores being composed of many cells), to which the 

 well-known smuts of rye and violets belong. The fungus 

 grows beneath the bark of the tuber, where it forms a 

 thin dark greenish-brown stratum, often extending over 

 the greater part of the external surface of the potato. The 

 presence of the fungus may be detected by discoloured 

 blotches on the bark. As in the disease caused by the 

 Peronospora, it often happens that no trace of the fungus 

 is to be seen at the time of harvesting. It frequently 

 shows itself during the winter in stored potatoes, which, 



