Sick Soils 



19 



The latest investigations have not yet disclosed 

 whether or not Pythium de Baryanum is carried over 

 from year to year by its oospores. It is apparently 

 able to propagate itself indefinitely by its vegetative 

 mycelium. 



Of the other fungi which are capable of pro- 

 ducing a damping off in the greenhouse or seed bed 

 may be mentioned Sclerotinia lihertiana Fckl., 

 Phoma solani Halst., Colletotrichum sp., Fusarium 

 sp., Sclerotium rolfsii Sacc. and Rhizoctonia solani 

 Kuhn. Each of these, except the last, will be taken 

 up separately in connection with the study of their 

 respective hosts. 



The fungi which cause damping off are introduced 

 into the greenhouse, primarily v/ith sick soil used in 

 the compost, and also with infected manure. The 

 practice of dumping diseased plants and all other 

 infected material in the manure pile cannot be too 

 strongly condemned. Sometimes very lightly infect- 

 ed plants with no visible symptoms of disease in the 

 seed bed may nevertheless act as carriers, and like- 

 wise infect the greenhouse soil. 



Damping Off of Cuttings 



Greenhouse men are often troubled with a damp- 

 ing off of cuttings. In specific cases this is brought 

 about by parasitic fungi which, however, will be 

 taken up at length under the discussion of the va- 

 rious hosts. 



