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. 462 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 
Fic. 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- 
