CHAPTER LI. 

 PLANT COMMUNITIES: SEASONAL CHANGES. 



494. Relations of plants. — One of the interesting subjects 

 for observation in the study of the habits and haunts of plants 

 is the relation of plants to each other in communities. In the 

 topography of the moors, and of the land near and on the 

 margins of bodies of water, we have seen how the adaptation 

 of plants to certain moisture conditions of the soil, and to 

 varying depths of the water, causes those of a like habit in this 

 respect to be arranged in definite zones. Often there is a pre- 

 dominating species in a given zone, while again there may be 

 several occupying the same zone, more or less equally sharing 

 the occupation. Many times one species is the dominant form, 

 while several others exist by sufferance. 



495. Plants of widely different groups may exist in the 

 same community. — So it is that plants of widely different rela- 

 tionships have become adapted to grow under almost identical 

 environmental conditions. The reed or grass growing in the 

 water is often accompanied by floating mats of filamentous algae 

 like spirogyra, zygnema; or other species, as cedogonium, coleo- 

 chsete, attach themselves to these higher lords of creation; while 

 desmids find a lodging place on their surface or entangled in 

 the meshes of the other algae. Chara also is often an accom- 

 paniment in such plant communities, and water-loving mosses, 

 liverworts, and fern-like plants as marsilia. Thus the widest 

 range of plant life, from the simple diatom or monad to the 

 complex flowering plant, may, by normal habit or adapted 

 form, live side by side, each able to hold its place in the com- 

 munity. 



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