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ANIMAL BIOLOGY 



A far more striking example of symbiosis is afforded by Lichens 

 which represent intimate combinations of various species of color- 

 less plants (Fungi) and simple green plants (Algae). In each case 

 the Fungus supplies attachment, protection, and the raw materials 

 of food, while the Alga performs photosynthesis. Each can live 

 independently under favorable conditions, but in partnership they 

 are superior to hardships with which many other plants cannot 

 cope, and thus some Lichens become the vanguard of vegetation 

 in repopulating rocky, devastated areas. (Fig. 221.) 



From the practical standpoint of agriculture the symbiotic 

 nitrogen-fixing Bacteria are of first importance. It will be recalled 



Fig. 222. — Rose Aphids visited by Ants. 



that these Bacteria form small nodules on the rootlets of higher 

 plants, such as Beans and Clover, and make atmospheric nitrogen 

 available to the latter - - return it to the cycle of the elements in 

 living nature. (Fig. 16.) 



Still another type of association in which both partners profit is 



