Violet Diseases 355 



Symptoms. Diseased plants are dwarfed, with 

 crinkled foliage, of a sickly yellow color. A closer 

 examination will show that the seat of the trouble 

 is confined to the underground stems and roots. In 

 damp soils the former are often cracked, distorted, 

 or covered with water-soaked spots. On the roots 

 occur numerous brown or black lesions which eventu- 

 ally girdle them. This girdling may take place at 

 several points. Often the roots rot off (fig. 73, a), 

 and all that remains is merely a short stub. The 

 runners like the roots are often spotted or girdled 

 in many places. The lesions. first appear as a brown 

 water-soaked spot which enlarges, the center becom- 

 ing whitish and the margin black. On the leaf 

 petioles lesions are often produced which are simi- 

 lar to those formed on the runners. 



The Organism. Thielavia hasicola has several 

 spore stages. The chlamydospores are composed of 

 from four to eight segments (fig. 73, e and f.). 

 The basal segments are usually empty. The others 

 above are dark brown, with thick walls and are able 

 to break up into individual cells each of which is 

 capable of germination. Another spore type is the 

 spore generating tube from within which are pushed 

 out small cylindrical bodies with thin walls, that are 

 known as endoconidia (fig. 73, c and d.). The 

 latter too are capable of germination. The third 

 spore form is the ascospores. These are borne in 

 sacks within a main globose fruiting body known 

 as the perithecium. The latter stage, however, is 

 seldom found on diseased violets. The fungus is 



