Minnesota Plant Diseases. 37 



half-saprophytes, since they are capable of attacking living fish 

 or other water animals. As saprophytes, however, the water 

 molds obtain their nourishment from the water in which they 

 are continuously bathed and in which organic food stuff is 

 found in solution. In stagnant pools or ponds they may be 

 particularly abundant. They are often sensitive to the amount 

 of acid in the water, preferring very slightly acid water. Such 

 plants have their food material easily accessible, absorbing it 

 at all points of the mycelium. 



Dung-dwelling habit. Very many fungi are constantly 

 found on the dung of certain animals. Particular fungi are 

 often to be met with only on the dung of certain species of 

 animals and on the other hand some are almost constantly to 



Fig. 16. — A dung-dwelling fungus (Pilobolus) of the black mold group, on horse dung. 

 The threads, bearing spore-cases, are seen pointing in parallel directions. Photograph 

 by F. K. Butters. 



be found on the dung of these animals if placed under proper 

 conditions. For instance, certain molds grow on fresh horse 

 dung and almost without exception one will find this fungus 

 if the horse dung is placed under favorable conditions of 

 moisture and heat. There are two ways in which the fungus 

 spores get into the dung of animals. They may fall on the 

 dung from the air or they may be deposited with the dung, 

 having previously passed through the alimentary canal. In 

 the latter case they are of course taken in with the food of 



