>66 



DISEASES OF CULTIVATED PLANTS 



their brown colour are apt to be overlooked, even when 

 abundant. 



Ascophore 1-3 cm. across, stem 2-7 cm. long; spores Sin 

 an ascus, elliptical, 15-18x6-7 ft. 



Collecting the ascophores tends to check the disease. 



Sclerotium disease (Sclerotinia sc/ero/ion/m, Massee) is 

 probably parasitic on a greater number of different kinds of 

 plants than any other fungus, members of all the families of 

 cultivated plants being attacked. White and swede turnips, 

 cabbages, carrots, broad and haricot beans, potatoes, cucum- 



FiG. jZ.SclerotiniascUroliorum. 1, part ol .1 



anthemum stem with black sclerotia of the 



fungus ; 2 n itium b jerous 



fruits; 3, ascus with spores. Figs. 2 and 3 mag. 



in is, melons, hemp, petunias, zinnias, and chrysanthemums 

 beinsr anions: the number of its victims. The disease coin 

 monly attacks the stem, commencing as a white mould at the 

 ground line and working upwards. When the parasite has 

 been at work for some Hum the leaves turn yellow and will, 

 and finally the stem collapses, death being due to lack of food 

 and water, owing to the mycelium of the fungus having 

 choked up the vessels, and thus retarded the passage of water 

 up the stem. When the stem is hollow the mycelium is pro- 

 duced in considerable quantity in the cavity, and forms la 



