STUDIES OF AMERICAN FUNGI. 



varieties, or may be species, among forms accredited by some to the 

 one species. 



The Gills. On the under side of the pileus are radiating plates, 

 the gills, or lamellcc (sing, lamella). These in shape resemble some- 

 what a knife blade. They are very thin and delicate. When 

 young they are pink in color, but in age change to a dark purple 

 brown, or nearly black color, due to the immense number of spores 

 that are borne on their surfaces. The gills do not quite reach the 

 stem, but are rounded at this end and so curve up to the cap. The 

 triangular spaces between the longer ones are occupied by succes- 

 sively shorter gills, so that the combined surface of all the gills is 

 very great. 



Figure i. Agaricus campestris. View of under side showing stem, annulus, 

 gills, and margin of pileus. (Natural size.) 



The stem or Stipe The stem in this plant, as in many other 

 kinds, is attached to the pileus in the center. The purpose of the 

 stem seems quite surely to be that of lifting the cap and the gills up 

 above the ground, so that the spores can float in the currents of air 

 and be readily scattered. The stem varies in length from 2-10 cm. 

 and is about i-i>4 cm. in diameter. It is cylindrical in form, and 

 even, quite firm and compact, though sometimes there is a central 

 core where the threads are looser. The stem is also white and 

 fleshy, and is usually smooth. 



The Ring. There is usually present in the mature plant of Agaricus 

 campestris a thin collar {annulus') or ring around the upper end of the 

 stem. It is not a movable ring, but is joined to the stem. It is very 

 delicate, easily rubbed off, or may be even washed off during rains. 



