262 GROWTH OF A MUSHROOM 



rather spherical in shape and so small that it is quite concealed 

 in the ground or by surrounding vegetation. When conditions 

 are favorable for further growth, as after a rain, each cell of this 

 miniature fungus absorbs moisture and rapidly expands, thus 

 causing the mushroom to spring up as by magic and reach its 

 full growth in a few hours. As the stipe elongates, the pileus 

 spreads out like an umbrella, rupturing the veil, a part of which 

 clings to the stalk (Fig. 170, A, a) in the form of a ring, the 

 annulus, and a part may also hang in the form of ragged fila- 

 ments from the edge of the pileus. If a volva is formed, this 

 is also ruptured by the elongation of the stipe, forming a cup at 

 the base of the stipe, and usually portions also remain attached to 

 the top of the pileus as scales and patches (Fig. 170, A, D). 

 The structure of the mushroom is very simple. The stipe con- 

 sists of a mass of nearly parallel hyphae that show little modi- 

 fication save at the surface of the stem, where they are sometimes 

 more compactly arranged (Fig. 171, A, B). By cutting across 

 the gills, so that we can look into the ends of them, it will be 

 seen that the hyphae extend down the center of the gills and also 

 continually radiate out on either side, forming a compact layer 

 of rather elongated cells on the surface of the gills, known as the 

 hymenium (Fig. 171, C). A magnified view of a portion of this 

 hymenium shows that it is composed of paraphyses and basidia 

 (Fig. 171, D}. These so-called paraphyses are potential basidia 

 and continue to develop as such during the life of the mushroom. 

 The basidia are not divided as in the smuts and rusts, but the 

 spores are formed in the same manner at the end of two or four 

 small tubes that grow out from the apex of the basidia. It 

 should be stated that a series of intermediate forms exist that 

 connect the divided basidia with the present form. The spores 

 are mature and begin to drop off as soon as the pileus opens, 

 when they are scattered byj:he wind and develop under favorable 

 conditions into a new mycelium. If the pileus of a freshly 

 opened mushroom is placed on a sheet of gray paper and tightly 

 covered with a dish, so as to exclude all air currents, the spores 

 will fall directly upon the paper and in a few hours form an 

 exact copy or a spore print of the gill arrangement. There 



