Minnesota Plant Diseases. 107 



seem to be stimulated for they now become the egg spores 

 whose special function is that of resting spores. They cannot 

 be made to develop further until they have rested for some 

 time. After this rest period they divide up internally into 

 swimming spores. 



These water molds grow luxuriantly on almost any kind of 

 decaying organic matter in the water. When the bodies of 

 dead insects, such as flies or grasshoppers, fall into the water 

 they soon become surrounded by a halo of fungus threads from 

 the water mold which quickly forms swimming-spore cases in 

 countless numbers. When the nutrient material becomes 

 scarce egg spores are produced. Dead minnows or fish are 

 also quickly attacked by these fungi and the rapidity with which 

 the fungus spreads is well seen in the growths on a fisherman's 

 minnow bait. Not only are dead fish attacked. When living 

 fish have suffered the loss of a few scales or some other slight 

 injury, the fish mold may gain entrance through this spot and 

 may spread rapidly as a parasite and finally kill the fish. It 

 may even gain entrance through the gills or in the eyes of the 

 fishes, and it very frequently attacks their eggs. The fish 

 molds therefore may become dangerous pests in hatcheries. 

 Numerous epidemics of these molds are known to have de- 

 stroyed myriads of fishes in their native streams and lakes as 

 well as in hatcheries. Not only fishes but other aquatic animals 

 such as mud puppies and probably other amphibians are sub- 

 ject to attack, as are also many of the tiny microscopic water 

 animals so abundant in stagnant pools and lakes, and thus the 

 fungus preys on the food of fishes. A few forms are known 

 which attack the pond scums. As is to be expected in such 

 plants, the parasite is not of a high type, i. e., no exact selection 

 of host seems probable though this simple method is highly 

 proficient in its own way. The proficiency is due largely, no 

 doubt, to the great number of swimming spores formed and the 

 rapidity of their formation. (Figs. 32, 33, 42.) 



Sewer and drain pipe molds (Saprolegniinea in part). It is 

 to be expected that sewer- and drain-pipes would offer favorable 

 habitats for fungi of the general habits of the water molds and 

 there are fungi which are constantly found in these places. A 

 large amount of decaying organic material is always present to- 



