APPENDIX A 



607 



The Lichens (ll' kens) constitute a striking example of intimate symbiotic 

 relations between two distantly related plants — one an alga and one a fungus — 

 by means of which the former obtains the necessary raw materials for photo- 

 synthesis and the latter receives a supply of manufactured food. Lichens com- 

 monly form irregular patches on rocks (Fig. 33.3), the bark of trees, or the soil. 

 These patches consist of a thallus, which may be thin and tightly applied to the 

 substratum, or rough, scaly, fibrous, leaflike, or pendulous. The color of lichens 

 is extremely varied, but gray-greens, browns, reds, and smoky colors predominate. 

 Each lichen consists of a single-celled green alga mingled with a mass of fungus 

 filaments; the two plants together form the thallus. The fungus filaments absorb 



Fig. A. 9. Higher fungi (basidiomycetes) . Left, a bracket fungus saprophytic on dead trees; 

 upper right, the poisonous Amanita muscaria; lower right, the edible meadow mushroom, 

 Agaricus campestris. (Left by Prof. E. B. Mains, the others by Prof. Alexander H. Smith.) 



water and dissolved substances from the substratum; the algal cells utilize these 

 materials for photosynthesis; and both plants make use of the manufactured food. 

 Alga and fungus reproduce independently of each other, and the lichen association 

 may also be propagated by joint vegetative methods. The algae and some of the 

 species of fungi that enter into these lichen associations may live apart from each 

 other; but man}' others of the fungus species that form lichens cannot survive 

 except in partnership with an alga. 



Phylum II. BRYOPHYTA (bri of i ta), Greek, brijon, "moss"; 

 phyton, "plant." 



The bryophytes (bri' o fits) form the second great division of the plant 

 kingdom, the group comprising about 17,000 existing species of liver- 

 worts and mosses. They are the simplest land plants, undoubtedly derived 

 from some group of green algae; but they differ from all thallophytes in 



