Hill: Penobscot Vegetation 393 



permanency of the water supply. A well-drained area dif- 

 fers from an undrained one in several respects ; the place 

 where it is developed ; the amount of underlying peat ; the 

 acidity of the soil; and the character of the plant covering. 

 The permanency of a lake or pond is controlled by the re- 

 lation between the topography and ground water level. 

 Where this relationship is such that water is present in a 

 closed basin throughout the year, a permanent lake or pond 

 is formed. Where water is present during the spring, but 

 absent at other seasons due to the lowering of the water 

 table or evaporation, a periodic pond results. In places 

 where the topography favors swamp formation and there is 

 abundant surface water throughout the summer due to a 

 high water table, a permanent swamp occurs. Swampy 

 areas which dry out during the summer may be found, but 

 these periodic swamps do not have as distinctive a type of 

 vegetation as do the other types of lowland mentioned. 



a. Association-types of permanent well-drained lakes, 

 ponds, and lake-swamps 



The succession of vegetation starting in a well-drained 

 lake or pond and leading to the formation of a forested area 

 has been one of the stock illustrations of ecologists for 

 many years and need not be discussed in detail. Briefly 

 six well-recognized stages occur, namely: (1) submersed 

 aquatics; (2) aquatics with floating leaves; (3) aquatics 

 with aerial leaves — these three stages comprising the lake 

 series; (-t) sedges; (5) shrubs; (6) swamp forest — the 

 latter three making up the swamp series. 



Association-types of the lake series 

 The nature of the aquatic vegetation in the ponds and 

 lakes of the Penobscot Bay region varies with the character 

 of the shores and bottom. In ponds with gravelly bottoms 

 there is apt to be no vegetation. Sandy bottoms on the 

 other hand support a few very characteristic species, while 



