io6 



Minnesota Plant Diseases. 



ever, all aquatic in habit and thrive in stagnant pools where 

 decaying animal and plant materials are particularly abundant. 

 They are typically half-saprophytes, passing most of their life 

 feeding on dead material in the water, but living parasitically on 

 fish or other animals, as occasion presents itself. As wa- 

 ter plants they utilize the swimming spores and these are usual- 

 ly formed in enormous numbers in spore cases of various 

 shapes. The swimming spores are of the same general struc- 

 ture as those of the lower algal fungi, though in a few cases 

 they seem to be unable to get out of their spore cases and they 



then grow out into 

 threads while still 



inside f the case 



and never develop 

 whips. All the fish 

 and water molds 

 develop breeding 

 organs of two kinds, 

 male and female. 

 The female organs 

 are usually spher- 

 ical cases, which 

 contain a small 

 number of eggs, 

 and the male organ 

 is an elongated 

 thread which is 

 sometimes branched 

 and usually arises 

 from the same 

 thread which pro- 

 duces the swollen 

 egg case. Now the 

 male thread pene- 

 trates the egg case 

 and can be seen 

 making its way between and around the eggs, but a remarkable 

 feature lies in the fact that they never as far as has yet been 

 observed breed with the egg cells. The latter nevertheless 



FIG. 42. Water and fish molds. 1. A fungus thread with 

 an unopened spore-case. 2. An opened spore-case 

 with the escaping swimming spores. 3. An egg-case 

 with the male threads penetrating it. The spherical 

 bodies in the egg- case become the resting egg-spores. 

 Highly magnified. 1 and 2, after Thuret; 3, after 

 DeBary. 



