46 Diseases of Truck Crops 



zoctonia for the first time. In the United States the 

 first extended account of the fungus was given by 

 Pammel. ' Many other excellent accounts by Amer- 

 ican workers have appeared from time to time, to 

 which we shall have occasion to refer later. 



The genus Rhizoctonia includes several forms of 

 sterile fungi, all of which are distinguished by their 

 manner of ^growth in pure culture, and by their 

 mycelium form. Yotmg hyphae of R. solani Kuhn 

 are at first hyaline, then deepen in color from a yellow- 

 ish to a deep brown. The young branches are some- 

 what narrowed at their point of union with the parent 

 hypha and. grow in a direction almost parallel to each 

 other (fig. 6 b). A septum is also laid down at a 

 short distance from the point of union with the par- 

 ent mycelium. There is another fortn of mycelium 

 which is made up of barrel-shaped cells, each of which 

 is capable of germinating like a spore (fig. 6 c, d). In 

 pure cultures R. solani produces sclerotia, which are at 

 first soft, whitish, and later become hard and dark. 

 The fungus is carried over from year to year as scler- 

 otia which are able to withstand the effect of heat, 

 cold, drought, or moisture. 



Parasitic Soil Fusaria 



Next in importance to Rhizoctonia is a group of 

 fungi which belong to the genus Fusarium. Lands 

 infected with these species of fungi become unfit for 

 cabbage, potatoes, tomatoes, etc., causing great finan- 



' Pammel, L. H., Iowa Agr. Expt. Sta. Bui. 15: 244-251, 1891. 



