266 



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 

 anascus, elliptical, 15-18x6-7 /*. 



Collecting the ascophores tends to check the disease. 



Sclerotium disease (Sckrotinia sclerotiorum, 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. 78. Scleroiinia sclerotiorum, i, part of a 

 chrysanthemum stem with black sclerotia of the 

 fungus ; 2, a sclerotium bearing five ascigerous 

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



bers, melons, hemp, petunias, zinnias, and chrysanthemums 

 being among the number of its victims. The disease com- 

 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 time the leaves turn yellow and wilt, 

 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 large 



