660 THE AGARICACEAE OF MICHIGAN 



PILEUS 5-15 cm. or more broad, compact, firm, convex then ex- 

 panded, obtuse, moist, glabrous or somewhat tomentose, white or 

 whitish, becoming dull leather color in age, sometimes with yellow- 

 ish or brownish shades, even on margin but often cracked in age. 

 FLESH white, thick. GILLS sinuate-adnexed becoming emarginate 

 or rounded behind, broad, close to subdistant, white or whitish. 

 STEM 3-7 cm. long, variable. 1-2 cm. thick, stout, solid, firm, eccen- 

 tric, straight or curved, glabrous, sometimes slightly or densely 

 tomentose, whitish. SPORES spherical, 5-7 micr. diam., smooth, 

 white in mass. ODOR and TASTE pleasant. 



(Dried: Brownish -tan throughout.) 



Solitary or caespitose. On decayed or living wood of elm, hick- 

 ory, maple trunks, etc.; often from a crack or wound of the living 

 tree. Throughout the State. September-November. Rather infre- 

 quent except locally. 



This Pleurotus apparently occurs only on frondose trees, especi- 

 ally on the elm — whence its name. It is not known whether it is para- 

 sitic on the living trees or not. Shade-trees in cities are frequently 

 its home. It is one of our best edible mushrooms when young, but in 

 age. it becomes somewhat leathery. Once located on a tree, it may 

 often be found fruiting in successive seasons. It often appears on 

 the pruned ends of branches, and may be found far up on the 

 tree. This species is largely free from grubs, especially in the late 

 fall, and often persists or dries in place. It forms a good article 

 of diet in winter, if it is collected when young and the caps are 

 dried. Some of its characters are quite variable. It may appear 

 in dense clusters, or only as a single individual. When growing 

 from the side of a trunk, the stems often grow downward ami the 

 cap develops horizontally. Others grow erect, especially when they 

 appear on top of the branch. When the plant grows to* consider- 

 able size, it is usually quite tomentose on the pileus and stem, 

 which normally are glabrous. The color is often quite deceptive. 

 Early, fast-growing individuals are pure white, but late, slow 

 growing ones become brownish or tan-colored; all of them tend 

 to become darker in age. The stems are mostly eccentric, but erect 

 plants may have central stems. The mode of attachment of the 

 ,ui I Is is the most important distinction between this species and 

 /'. ostreatus and I>. sapidus; for although the latter have short 

 and lateral steins. P. ulmarius also may have stunted stems grow- 

 in- far to one side. As all of them are equally edible, this point 

 is only of diagnostic importance. Several varieties have been de- 

 scribed, based on the variations mentioned above. 



