354 George E. Nichols, 



drained ponds, since essentially the same end is accomplished 

 through the periodic drying up of the pond as might be attained 

 through drainage. They therefore reqviire no special comment. 



2. The Formation-types of Lake- and Spring-swamps 



Inland 



a. INTRODUCTORY 



Lake-, spring-, and precipitation-swamps. — Swamps which 

 have originated in the manner described earlier, through the 

 filling in of lakes by vegetation, may be designated Lakc-szvamps. 

 Many swamps, however, probably the majority of those in the 

 lowland, owe their existence to the relation between topography 

 and ground water level, i. e., to the presence of spring or seepage 

 water. Such swamps may be designated Spring-szvamps (see 

 Nichols '15, pp. 184, 192). Lake- and spring-swamps are wide- 

 spread in their distribution throughout most regions. In regions 

 like the one under consideration, where precipitation is high and 

 the evaporating power of the air low, there is still a third type 

 of swamp whose existence is dependent very largely on direct 

 atmospheric precipitation. Swamps of this sort, well exemplified 

 by the raised bogs of the high interior plateau, may be desig- 

 nated Prccipitation-szvamps. 



The ecological significance of drainage. — In his study of the 

 geographical distribution and ecological relations of bog 

 associations in eastern North America, Transeau ('03, p. 420) 

 arrived at the conclusion that "the 'drained swamp' and 

 'undrained swamp' classification will not hold over any great 

 area." Drainage, however, has been employed as a basis of 

 classification by Cowles ('01, pp. 145-156) and others, and it is 

 the conviction of the writer that, from the standpoint of physio- 

 graphic ecology, this factor affords by far the most fundamental 

 criterion yet conceived, at least for the classification of the lakes 

 and swamps in the inland group. The relationship between 

 cause and effect may often be obscure, since the influence of 

 drainage is commonly expressed indirectly through other, more 

 direct factors ; but, in the last analysis, drainage, more than any 

 other single factor or set of factors, seems to have a vital 

 influence on the vegetation, through its effect on the aeration of 

 the soil and on the accumulation therein or removal therefrom 



