A MUSHROOM 75 



sites on the roots or other parts of living trees. What we 

 ordinarily call a " mushroom " is merely the part of the 

 fungus that grows above ground and bears the spores ; it is 

 the fni iting body of the plant. The vegetative body, like that of 

 the bread mold or the rust, consists of colorless or whitish 

 branching threads which live for the most part underground. 

 Some of them are combined into thicker strands, but these 

 strands, as well as the separate threads, are delicate and 

 easily broken when the soil is disturbed. For this reason 

 we usually see little or nothing of the vegetative body of the 

 mushroom, excepting some fragments that remain attached 

 to the fruiting body when the latter is pulled from the soil 

 (Fig. 33). The threads, like those of smuts and rusts, are 

 made up of rather short ceUs joined end to end. They attach 

 themselves to particles of dead organic matter with which 

 they come in contact in their growth through the soU, and 

 digest such parts of these substances as they can use for food. 



104. Fruiting Body. — In the summer or fall, after the 

 plant has been growing for some time, smaU knots appear 

 upon it here and there, near the surface of the soU. These 

 knots are composed of some of the branches of the fungus 

 which are beginning to pack themselves more closely together. 

 Each knot is the beginning of a fruiting body. The threads 

 composing the knot grow and branch, and so the knot de- 

 velops into a firm, rounded " button." By further growth 

 this button develops into the fruiting body of the mushroom 

 (Fig. 34). It becomes divided into an upper part which is 

 to form the cap, and a lower portion, the stalk. The margin 

 of the cap is at first attached to the stalk by a thin membrane, 

 the veil, which hides the lower side of the cap where vertical 

 folds or gills are being formed. 



When the fruiting body reaches nearly its full size, the 

 margin of the cap, which until now has been curved down- 

 ward and inward, begins to spread outward ; this makes the 

 cap flatter on top, and causes a pull on the veil ; the veil is 



