Unity and Interdependence in Living World 653 



considered in detail in another chapter. Frequently, we classify living 

 organisms into different communities because of their habitats (where 

 they live). Animals that live on land are terrestrial (Gr. terra, land); 

 those that live in water are aquatic (L. aqua, water) ; and those that live 

 in water and on land are amphibious (Gr. amphi, both; hios, life). 

 Plants may be classed as water plants or hydrophytes (Gr. hydro, water; 

 phyton, plant) ; land plants or terraphytes; desert plants or xerophytes 

 (Gr. xeros, dry; phyton, plant) ; plants requiring moderate moisture are 

 mesophytes (Gr. mesos, moderate or middle; phyton, plant). Living 

 plants and animals may be divided into such communities as seashores, 

 fresh waters, forests, grasslands, deserts, etc. 



Fig. 326. — Balance in Nature as rev^ealed by a diagram showing the food inter- 

 relationships in a hypothetical prairie community. All living things depend on 

 other living things for various things, including food. The arrows point toward 

 the organism which uses the other organism as a source of food. (Redrawn and 

 modified from Shelford ; from Potter: Textbook of Zoology, The C. V. Mosby Co.) 



Animal and plant communities are never constant or static but are 

 continually changing. These changes in individuals, or in the com- 

 munity as a whole, are the attempts on the part of living organisms to 

 adjust themselves successfully to their changing, nonliving, and living 

 environments. The introduction, naturally or artificially, of new species 



