PLANT FORMATIONS. 521 



vegetation of the sandy beach or strand; 3d, the vegetation of 

 the "bad lands" and alkali marshes. 



992. Close edaphic formations. While these are controlled 

 by conditions of the ground, these conditions are not so austere 

 as to prevent the development of a close growth. In the forest 

 region too much water in the soil may prevent forest growth, but 

 encourages a rank growth of marsh plants. Some of the ex- 

 amples of close edaphic formations are: ist, mud or reed-swamp 

 formations; 2d, meadow-swamp formations; 3d, sphagnum 

 moor formations. The "park-like forests" along river bottoms 

 in the prairie region or the "oases" in deserts are close edaphic 

 formations in these regions, since they are not developed in 

 response to the climate, but in response to a condition of the 

 ground (the abundance of ground water), although the type 

 of the vegetation is really that of the forest. 



III. Aquatic Formations. 



993. These are represented by the vegetation in ponds, lakes, 

 streams, and in the ocean. The vegetation is of a type very 

 distinct from the climatic or edaphic. The formations occur 

 as patches or strips infiltrated in the climatic and edaphic for- 

 mations, and also as a fringe along continents, islands, or bodies 

 of land bordering deep and large bodies of water. The character 

 of the vegetation is hydrophytic or halophytic, according to its 

 occurrence in fresh water or salt water. There are, therefore, 

 two grand subdivisions: ist, fresh water or limnetic formations; 

 2d, salt water or pelagic formations. 



IV. Culture Formations. 



994. This type of vegetation is developed in response to the 

 work of man in the cultivation of the soil, or as a result of his 

 interference with the development of the climatic type of vege- 

 tation. Man overcomes the climatic factor by removal of the 

 climatic vegetation type and by the cultivation of the soil; in 



