PLANT SUCCESSION 511 



other representatives of swamp societies. Through the growth 

 of the swamp societies, the swamp is finally so filled up that it 

 is transformed into a mesophytic area, and the plants of the 

 swamp societies are succeeded by Mesophytes (Figs. J$2 and 

 463). It is obvious that the hydrophytic societies have been 

 exceedingly important factors in transforming lakes, ponds, and 

 old river beds into tillable land, and the fertile soil of such 



FIG. 462. A succession of plant societies, showing transition from hydro- 

 phytic to mesophytic societies. The successive societies are as follows: 

 Pond Lily Society, Sedge Society at the margin of the pond and grading into 

 a Swamp Grass Society further back, a shrub society still further back, and 

 finally in the background a mesophytic forest society. From Coulter, photo, 

 by Lewis. 



areas is largely due to the humus added through the decay of 

 the hydrophytic societies. On sand dunes, beaches, ground 

 cleared and allowed to grow up again, and most everywhere one 

 can observe plant succession. On sand dunes around the Great 

 Lakes, for example, Poplars are succeeded by Pines, which are 

 in turn succeeded by Oaks and other deciduous trees. 



Studies of successions and societies give us very useful in- 



