Minnesota Plant Life. 45 



Fly-cholera fungi. Related to the moulds are the singular 

 fly-cholera fungi. Many persons will have noticed sticking to 

 the window-panes in autumn the dead bodies of flies surrounded 

 for some distance by a faint yellowish film upon the glass. This 

 film consists of spores of the fly-cholera fungus which have been 

 shot into the air by a mechanism similar to that described for the 

 pill-throwing mould. The vegetative body of the fly-fungus 

 lives within the body of the fly where, growing luxuriantly, it 

 interferes with the life-processes of the insect, kills it, and con- 

 verts a large portion of its body into food for its own use. Other 

 flies approaching the infected individual are peppered with the 

 tiny spores of the fungus, or they receive the contagion while 

 walking upon an infected window pane or in a spore-strewn cor- 

 ner. In this way every autumn unnumbered millions of flies 

 are killed. A closely related cholera-fungus attacks the Rocky 

 mountain locust and is of great economic importance because it 

 keeps this dangerous insect in check. Still other varieties 

 attack other insects, but these two will serve as examples. 



Cell-parasites. There are a large number of microscopic 

 algal-fungi of very curious behavior. Some of them find their 

 way into the skin-cells of flowering plants and there live as para- 

 sites, while others insinuate themselves into the eggs of algae 

 and devour them. Some of them are found in the soft sub- 

 stance of swamp plants ; some may be discovered in pond-scum 

 filaments where they consume the cell-contents ; some find their 

 way into desmid cells and destroy them ; some enter the pollen- 

 grains of flowering-plants, notably of the pines, and feed upon 

 the living contents. They invade the diatoms and various 

 algae; they infect the spongy tissues of the peat-mosses; they 

 penetrate the wall of fish-mould eggs and by their omnivorous 

 habits impress it upon us that no organism is too small or incon- 

 spicuous to escape its enemies. 



Fish-moulds. Related to the fungi which sometimes injure 

 their eggs are those surprising organisms, the fish-moulds, that 

 are often found forming gray fur coats on the bodies of dead 

 minnows or dead frogs. They are especially unwelcome in fish 

 hatcheries where they attack the eggs of the fish and destroy 

 them. Some varieties are found upon the dead bodies of aquatic 

 insects and others grow upon decaying substances when sub- 



