FLOWERLESS PLANTS. 183 



grown specimen, shows where this covering, called the 

 volva, was attached. The stout stem is called a stipe, and 

 its cap the pileus. Along the under surface of the pileus 

 you see numerous thin plates, called gills, and it is within 

 these plates that the spores are found, many thousands 

 occurring on the gills of a single mushroom. 



Puff-balls are mushrooms without the stem and pileus. 

 The " smoke " which escapes when they are broken con- 

 sists of spores, which are so exceedingly small that they 

 may penetrate everywhere. A few species of fungi are 

 good to eat, but many are poisonous, and to be avoided. 

 Yeast, mildew, smut, mold, and dry rot, all belong to this 

 group of plants. 



The gray, yellow, or greenish, crust-like layers that are 

 seen on stones and the bark of trees, on old walls, and in 

 rocky places, are a low form of vegetation, called lichens 

 (Fig. 478). They have little distinction of parts, except 

 that of upper and under surface, and certain specialized 

 places in which spores are formed. Alga, or the sea- weed 

 family, is another order of flowerless plants, which con- 

 tains many fresh-water species. The green scum seen on 

 the surface of stagnant water is one of the lowest forms of 

 fresh-water algae, called conferva. 



