10 THE AGARICACEAE OP MICHIGAN 



of the hyphae just inside the hyuieuial layer termed the sub- 

 hymeitium. 



The hymenium may include, along with the basidia, cells of 

 other shapes or functions; the cystidia (singular, cystidium), (see 

 Fig. 3, 40-44) are elongated, cells fusiform, lanceolate or have vari- 

 ous shapes according to the species, and project at maturity above 

 the basidia. Their function apparently is to aid in the exudation 

 of water from the plants. (F. Knoll, Jahrb. Vol. 50, p. 453.) The 

 presence or absence of cystidia is much used to identify certain 

 species. The observations must be carefully made, however, since 

 they quickly collapse at maturity in some cases, and in others do not 

 elongate uutil full maturity of the mushroom. They occur more 

 or less scattered over the surface of the gills and are often tipped 

 with oxalate of lime crystals. Also, they may occur on the edge of 

 the gills and give this a minutely flocculose or fimbriate appear- 

 ance. More frequently the edge is provided with elongated sterile 

 cells of various shapes which produce the same effect as cystidia. 

 In this work these are the only "sterile cells" referred to in the 

 descriptions. 



The spores vary in size, shape, color, structure of surface, etc.. 

 and are fully discussed under each group. (See Fig. 3, 1-34.) 



The stem, volva and anmilus are also described under each genus 

 possessing them. 



HABITAT AND GROWTH CONDITIONS OF THE AGARICS 



The Agarics, like all fungi, are either saprophytic or parasitic. 

 They are dependent on organic matter for a large part of their 

 food; this is due to the absence of chlorophyll which makes them 

 incapable of manufacturing carbon-compounds from the air. As 

 saprophytes they occur ou a great variety of substrata ; soil, 

 humus, dung, wood, fallen leaves, bank, straw, dead animal re- 

 mains, decaying fungi and forest debris of all sorts. They can even 

 be cultivated in the laboratory on gelatine and agar with proper 

 addition of sugars, etc. As parasites they are found on living trees 

 or shrubs, rarely on herbs. They are often attached to the rootlets 

 of trees and shrubs on which they cause formation of mycrohiza; 

 some consider this relation a parasitic one. 



tThe fleshy fungi are most abundant in woods and forests and 

 hence are largely dependent upon the character of the forest. 

 When the woods are cleaned or the forest cut down, there is often 

 quite a change in the flora of such a place after a few years. In, 



