438 NATURE STUDY AND LIFE 



An abundance of these plants will probably occur on the 

 stones in the fernery or on the tree trunks in the school 

 yard. It is not intended, for these elementary lessons, that 

 any of the different species be learned, for we have no 

 common English names with which to designate them. 

 There are 5600 named species, but it will be sufficient if the 

 class study and draw two or three of the commonest in the 

 neighborhood and learn to associate the name "lichen" with 

 them. It may be possible to explain to the class that 

 a lichen consists of two different plants living together : 

 a white fungus, consisting of a felt work of minute threads, 

 such as we shall see in the moulds and mushrooms ; and 

 much smaller, generally greenish plants, algae, entangled 

 in the meshes of the fungus. The fungus furnishes sup- 

 port and moisture to the algae, and, in return, the algae by 

 means of their green coloring matter and sunshine supply 

 food to the fungus. The algae can live without the fungus, 

 for they can find support and moisture for themselves, but 

 the fungus invariably dies if deprived of the help of the 

 algae, for it cannot get food enough from the stone to which 

 it clings, and without chlorophyll it cannot draw food from 

 the air by the aid of light. From this point of view the 

 lichens serve as an introduction to the two next plant 

 groups, the algae and the fungi. 



Algae. We can always find algae in the school aquaria, 

 often as incrustations or velvety growths on the glass, or 

 as green slimes attached to the plants or floating on the 

 surface. Snails, tadpoles, and clams will be required to 

 keep the aquarium clear. Algae vary in size, from plants 

 as small as a fern spore to the large brown rockweed, fucus, 

 that clings to the rocks and piles all along the coast. As 



