1 8 



Minnesota Plant Diseases. 



out one or more little tubes which elongate and finally, by 

 branching, produce numerous threads; the spore is then seen 

 at the center of a system of radiating threads, like the hub 

 of a wheel and its spokes. These threads soon branch pro- 

 fusely and now a circular, densely interwoven network is 

 produced which keeps on enlarging, thus encroaching upon 

 new- areas of nu- 

 trition. If the 

 spore should be 

 placed in nutrient 

 jelly, where its' 

 environments in 

 all directions are 

 alike, the result- 

 ing mycelium 

 would be ball- 

 shaped in outline ; 



but if the myceli- 

 um is nrodnrerl FIG. 7. Highly magnified view of section through end of 



mycelial strand of honey-colored mushroom, showing 

 in cii^1i n n1arp> nc compactness of central portion (c and d) and loose 



threads at the surface (a and b). Highly magnified. 



the mold soil on After z op f. 



the forest floor, the symmetry of the form is interfered with 

 by various obstacles. In general, a mycelium would tend to 

 become circular in outline as seen from above. Such a myce- 

 lium is often seen in the production of what are called fairy 

 rings. Many gill-fungus mycelia grow from year to year and 

 at the proper season of each year produce a crop of fruiting 

 bodies at the surface of the ground. These are formed at the 

 end of the mycelium and hence come to stand in a circle. One 

 circle appears each year, becoming larger year by year. 



The peculiar life habits of many fungi bring with them 

 peculiarities in the development. Many fungus spores will ger- 

 minate between temperatures a little above freezing, i.5-2C., 

 and 40-43C., but best at about 25C. Such as are required 

 to pass through the alimentary canal of certain animals before 

 germinating demand, in general, higher temperatures. One 

 of the gaseous constituents of the air, oxygen, is necessary to 

 the germination of spores of fungi. Every housewife knows 



