44 Diseases of Track Crops 



ops as a terminal enlargement which is cut oflE by a 

 septum from the mother thread. Next or adjacent 

 to it a. slender tube is cut off from the mycelitun by a 

 septum. This tube now performs the fimction of the 

 male sexual organ and is known as antheridium. 

 The latter then comes into close contact and empties 

 all.its content into the oogonium (fig. 5 d). Fertiliza- 

 tion thus takes place, and a mature egg or oospore 

 or winter resting spore is formed (fig. 5 e). 



The latest investigations have not yet disclosed 

 whether or not Pyihium de Baryanum is carried over 

 from year to year by its oospores. It is apparently 

 able to propagate itself indefinitely by its vegetative 

 mycelium. The seedlings of the following truck crops 

 are subject to damping off by Pythium : Beans, beets, 

 cabbage, cauliflower, endive, lettuce, pumpkin, tom- 

 ato, and turnip. 



Of the other fungi which are capable of producing a 

 damping off in seedlings may be mentioned; Sclero- 

 tinia libertiana Fckl., Phoma solani Halst., Colle- 

 totrichum sp., Fiisarium sp., Sclerotium Rolfsii Sacc, 

 and Rhizoctonia solani Kuhn. The first five will be 

 taken up separately in connection with the study of 

 their respective hosts (see pages 45, 46, 143, 305, 324). 



Other Soil Diseases 



We have seen that Pythium de. Baryanum is most 

 active as a disease on young seedlings. Other fungi, 

 however, may attack not only seedlings, but also 

 older plants, in various stages of development. As 



