FLOWEELESS PLANTS. 193 



within these plates that the spores are found, many 

 thousands occurring on the gills of a single mush- 

 room. 



Puff-balls are mushrooms without the stem and 

 pileus. The " smoke " which escapes when they are 

 broken consists of spores, which are so exceedingly 

 small that they may penetrate everywhere. A few 

 species of fungi are good to eat, but many are poison- 

 ous, and to be avoided. Yeast, mildew, smut, mould, 

 and dry rot, all belong to this group of plants. 



FIG. 855. 



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. They have little distinc- 

 tion of parts, except that of upper and under surface, 

 and certain specialized places in which spores are 

 formed. Algce, or the sea-weed family, is another 

 order of flowerless plants, which contains 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. 



