A MUSHROOM 



77 



pink if broken. The gills are at first flesh-colored or pink, 

 gradually changing, as the fruiting body grows older, to dark 

 brown or black. The stalk is white, and from two to four 

 inches high. 



105. Structure of the Fruiting Body. — In a thin section of the 

 stalk, examined under a low power of the microscope, one sees many 

 cells of diflFerent shapes. From the way in which the fruiting body 

 has been developed, we know that 

 these are the cells of the separate 

 threads that make up the fruiting 

 body, cut across in various ways. 

 Such a structure as this, composed 

 of threads closely packed together, is 

 sometimes called a false tissue, to dis- 

 tinguish it from the true tissues which 

 make up the bodies of the higher 

 plants. The cap of the mushroom is 

 composed likewise of a false tissue. 

 A section through the cap which cuts 

 a gill crosswise shows how the spores 

 are formed (Fig. 35). Each surface 

 of the gill is made up of a layer of 

 rather long cells that are perpendicu- 

 lar to the surface. Some of the ceUs 

 of this layer are rather slender ; 

 others, when they reach their fuU 

 size, are much broader. Each of the 

 broad cells of the surface layer is a, 

 basidium. From the end of each basidium four slender projections 

 grow out ; the outer end of each projection swells and is cut ofi by a 

 wall, so becoming a spore.' 



106. Distribution and Germination of Spores. — When the 

 spores are ripe they are shot oflf from the short stalks on which 

 they were borne. This shooting seems to be caused by a 

 sudden bulging of the wall at the end of each stalk. By 

 this means the spores are thrown far enough so that they may 

 fall -ndthout touching any of the neighboring basidia. Being 



1 In some cultivated varieties (perhaps all) of the field mushroom, and occaaon- 

 ally in wild races, each basidium forms only two projections and two spores. 



u3ym 



B 

 Fig. 35. — A, section through 

 a gUI, showing the arrangement 

 of threads and basidia. B, a 

 group of basidia of different ages, 

 showing their attachment to the 

 threads of the fungus, and the 

 way in which spores are formed. 



