4 THE AGARICACEAE OF MICHIGAN 



example, in a park, lawn, fallow field, roadside or in woods, may be 

 considerable, extending- underground for rods, so that the size of 

 the plant in the vegetative stage, in a linear sense, is quite large. 

 Under such permanent conditions, quite a number of species form 

 "fairy rings'* when they fruit. The mycelium is started at one 

 point and if the soil is favorably homogeneous in every direction, 

 growth continues radially from the original point and at the cir- 

 cumference of this patch of mycelium, where growth activity is 

 greatest, the fruit-bodies appear each year. In one case 5 "ring"' 

 with a diameter of 65 feet was observed by MacQuan in Africa. 

 (Grevillea, 1880-1881.) The appearance of the fruit-bodies of some 

 species "in troops" is usually due to the fact that only one arc of 

 the circle is left. In the forest, obstacles are too numerous so that 

 the •'ring'' does not remain perfect and the fruit-bodies appear 

 scattered promiscously. Observations made in a clean forest in 

 Europe for a period of ten years showed that the "ring" of some for- 

 est species traveled radially for several rods but the periphery at 

 length became obscure. The mycelium of many species doubtless 

 is more affected by irregularities in the food supply and hence grows 

 in an unequal manner, or produces such few fruit-bodies that the 

 radial growth does not show. Doubtless also where there are scores 

 of different kinds growing in a small area they intertwine or inter- 

 fere with each other. During continued wet weather the compressed 

 masses of- fallen leaves in frondose woods are often found to harbor 

 patches or sheets of mycelium of many species, which are easily ob- 

 served by removing the top layers of leaves and which are a fore- 

 runner of a good crop of fruit-bodies if the humidity is maintained. 

 Curious sheets of mycelium, of the appearance of sheets of paper, 

 are sometimes found between planks or other piled up lumber, but 

 these usually belong to the Polypore group of fungi. 



The Fruit Body 



The fruit-body, or carpophore, is the portion popularly referred 

 to as the mushroom, but it must be remembered that it is only a 

 temporary product of the plant as a whole, just as is the apple 

 of the tree which bears it. It is usually composed of the pileus or 

 cap. lamellae or gills, and a stipe or stem; in the genera Amanita, 

 Amanitopsis and Volvaria there is present in addition a universal 

 >■< i! which breaks away and forms a volva on the stem. In Amanita, 

 Lepiota, Armillaria, Pholiota, Cortinarius, Stropharia, Chamaeota 

 and slightly in a few other genera, there is found a partial veil, 



