84 THE AGARICACEAE OF MICHIGAN 



most closely related to Russula, from which it differs by the exuda- 

 tion of a milky or colored juice from the gills and elsewhere when 

 wounded. The abundance and size of many species which are edible 

 makes this an important genus economically; but a number of 

 species are believed to be poisonous and must be carefully dis- 

 tinguished. 



The PILEUS may be white, yellow, orange, green, blue, reddish, 

 tan, gray, etc., often with the colors in variegated zones of related 

 hues. It is either dry or viscid, glabrous, velvety or tomentose, and 

 the margin which is at first involute is usually much more velvety 

 or tomentose than the center of the pileus ; in some species, however, 

 the margin is naked. The GILLS are usually adnate at first or 

 acuminate on the stem, becoming spuriously decurrent in many 

 cases as the margin of the pileus is elevated at maturity or in age. 

 They are usually rigid-brittle, and exude the milky juice to best 

 advantage when quickly cut by a sharp-pointed instrument. They 

 are usually of unequal length and often forked, sometimes dicho- 

 tomously as in />.. piperatus. The color of the gills varies from 

 white to yellowish or grayish, and in many cases they become dis- 

 tinctly darker in age, a character on which the main division has 

 been based. In one group they become dusted by the spore* and are 

 said to be pruinose in age. The STEM has a rigid cortex with a 

 spongy-stuffed interior, and becomes rather brittle. It is never 

 fibrous but may become hollow or cavernous with age. It is either 

 white or has the color of the pileus, but often diluted. Its rigid, 

 stiff-looking appearance, which is due to the vesiculose structure of 

 the flesh, gives both the species of this genus as well as those of 

 Russula a characteristic pose by which these two genera are soon 

 easily recognized. The TRAMA has a structure which, along with 

 that of the Russulas, is unique among the Agaricaceae. The hyphae 

 of the usual slender, filamentous type of other genera are rather 

 scanty, and interweave among clusters of thin-walled, parenchyma- 

 like, isodiametric cells, forming the so-called vesiculose tissue. 

 Mixed with the filamentous are the milk-bearing hyphae, called 

 "latex-tubes" or "lactiferes." These extend longitudinally up 

 through the stem, spread out in the pileus and extend through the 

 gills. The "MILK," as it is called, is usually white as it comes from 

 a sudden wound, but in several species it is colored blue, orange or 

 red. After the white milk is exposed to the air for a few minutes, it 

 either remains unchanged or becomes yellow, lilac, pink, greenish 

 or grayish. In many species this change is only noticeable where 

 the milk touches the flesh, and the latter takes on the corresponding 



