Violet Diseases 361 



"5. Not giving the proper attention to the selec- 

 tion and preparation of the soil, to date and method 

 of planting, and to care and cultivation of the plants 

 during the growing season. 



"6. Not giving due consideration to the several 

 varieties and their adaptability to the soil and lo- 

 cation in which they are grown." 



It is evident therefore that these are important 

 points to which the grower must give careful atten- 

 tion. In addition and as far as possible preference 

 should be given to those varieties which are resistant 

 to leaf spot. Marie Louise, for instance, is a very 

 susceptible variety. On the other hand. Lady Hume 

 Campbell is said to be resistant. 



Since the spores of the causal organism may be 

 introduced with the soil, steam sterilization is rec- 

 ommended. Proper attention also should be given 

 to the ventilation, watering, and heating of the 

 houses. 



Cercospora Leaf Spot 



Caused by Cercospora viola Sacc. 



The trouble is characterized by large, dead, ashy 

 spots on the leaves (fig. 74, d.). The centers of 

 the spots are darker, due to the presence of the co- 

 nidiophores. These are dark and short. The conidia 

 are rod shaped, hyaline, long, slender, and many 

 septate. 



Root Rot 



Caused by Fusarium viola Wolf. 



Symptoms. This disease is characterized by a 



