GENERAL INTRODUCTION 13 



The rotting of cut or structural timber by the mycelium of some 

 Agarics is perhaps equally Important. Bridge timbers, railroad 

 ties ;i!ul even house timbers may be attacked. Pholiotn aeruginosa 

 is perhaps a much greater enemy of railroad ties than the rare 

 occurrence of its fruit-body would indicate. Lentinus lepideus has 

 Long been known as a destructive agenl to ;ill Borts of timber. Fire- 

 wood It'll in ilif woods iii moist situations, even if piled up, may be 

 attacked by a greal variety of the smaller Agarics. There can be 

 no doubt thai fungi of all soils, including Agarics, are exteng 

 agents of decay and are much more effective than bacteria in bring- 

 ing aboul the disintegration of dead vegetable matter ;ni«l thus 

 returning it to ilic soil ; it is only in the later stages of decav thai the 

 bacteria play the greater role. 



Agarics may show ;i decided preference for ;i certain substratum, 

 e. .u - .. kind of wood, kind of dung, kind of leaves, etc.. on which they 

 grow. Sonic are sharply limited to coniferous wood and are Q< 

 found on wood of broad-leaved trees, others seem to thrive well 

 on a greal variety of substrata. A lew are parasitic on other mush- 

 rooms. I Sec X\ ctalis. i The held mushroom Psalliota arvensis and 

 the common mushroom Psalliota campestris are scarcely ever found 

 in the woods, just as Cortinarius arimllatus is never found in the 

 tield. Some consider that the soil is here the controlling factor. It 

 must he remembered, however, that it is decaying vegetable food, 

 which is the foundation of the subsistance of the mushroom, and 

 the presence of barnyard manure or the fact that sheep have pas- 

 tured in a tield is after all more effective than the mineral content. 

 This question is not yet settled ami French mycologists lay quite 

 a little stress on the mineral content id' the soil, insisting that cal- 

 careous soil and clay soil are the homes of dillerent specif-. With 

 regard i<» Michigan species, the data are not sufficiently clear. 



THE DISTRIBUTION OP AGARICS IN MICHIGAN 



Any attempt to give a definite account at (he present lime of the 

 distribution of species in the stale is fraught with difficulties. 



.Many localities have not 1 n visited, and only a prolonged study 



of a locality reveals an approximation of the species occurring 

 there. The very fascination of the search for fungi consists p, their 

 sporadic appearance. The species appearing one season may he 

 absent the next. Some species fruit apparently only at long in- 

 tervals; others only under special weather conditions. 



The principal points in the state around which sufficient colh 



