Violet Diseases 353 



Downy Mildew 



Caused by Peronospora viola De By. 



Downy mildew produces indefinite spots on the 

 leaves. In general appearance this trouble resem- 

 bles that of the grape. The downy pale violet growth 

 on the spot consists of a layer of the conidiophores. 

 These are short, many times branched with small ul- 

 timate branchlets. The conidia are short and ellip- 

 tic. 



Smut 



Caused by Urocystis viola (Sow.) F. de W. 



Symptoms. The disease produces prominent ir- 

 regular swellings or blisters on root stalks, stems, 

 petioles, and leaves. Soon the swellings rupture, 

 exposing black-brown masses, and giving the aflFected 

 plant a smutty appearance. 



The Organism. The spore balls are reddish brown 

 and oblong to partly spherical. The sterile cells 

 are yellowish with age, but the fertile cells are red- 

 dish to light brown. The chlamydospores appear in 

 balls of 4 to 8 spores. 



Control. Smut is usually brought in with in- 

 fected cuttings or plants from out-of-doors. These, 

 therefore, should be avoided. Infected plants should 

 be destroyed by fire. 



Rust 



Caused by Fuccinia viola (Schum) D. C. 

 Symptoms. The rust is characterized by circular 



