PLANT FORMATIONS. 



dition and environment. Ground is here used in a broad sense 

 to mean the earth substratum in or upon which the plants grow, 

 and includes water areas as well as land areas. In this sense 

 different plant societies occupy somewhat distinct physiographic 

 areas, as marsh, moor (or bog), strand, rocky areas, sandy 

 areas, ponds, lakes, etc. These areas may be quite limited 

 in size, or they may cover many thousands of square miles. 

 The territory of a plant society, then, is in many cases coincident 

 with the territory of a single area of the edaphic formation, or 

 equivalent to the area of a principal formation. But the term 

 society is generally used in a broader sense than formation, which 

 refers more to the dominant vegetation. 



998. The individual formation. In each plant society, while 

 the general aspect of the vegetation is the same, there are certain 

 limiting factors which give it a more or less variegated appear- 

 ance. These factors are of two kinds: ist, the physical, which 

 relate to the variation in ground water, and to physical and 

 chemical conditions of the soil; and 2d, biological, which relate 

 to the struggle between different species to occupy the same 

 patch of ground. Distinct groups of vegetative elements are 

 thus formed in a society because in certain more or less limited 

 areas one or several species are dominant and give a charac- 

 teristic physiognomy to the area. Such a group in a society is 

 called a formation.* In reality the different formations re- 

 semble pieces of mosaic, when arranged without order, or zones 

 when arranged regularly where there is radial or lateral topo- 

 graphic symmetry. This is well illustrated in certain marshes, 

 or in shallow water, along margins of lakes, where there are 



* Formation is used in this sense by some, while others use here the 

 term association, reserving the term formation for a group of associations, 

 i.e., a principal formation. But the term association itself does not seem 

 well chosen. The word seems more applicable to certain "associations" 

 in a society or formation, i.e., certain of the subordinate members (ex- 

 ample, lianas, epiphytes, or other subordinate members). Some even pro- 

 pose the word society for epiphytes and lianas, and cite Schimper's use 

 of it in this connection. Schimper uses for epiphytes the term Genos- 

 senschaft, which means rather an association or guild. 



