104 J. E. CRIBBS 



stabilized, but the depressions between the hummocks are 

 commonly flooded in the spring and may remain so for most of 

 the summer, in which case vegetation is limited almost exclus- 

 sively to the hummocks or is composed of aquatics. The species 

 at this stage of the series include, Rosa Carolina, Cornus stoloni- 

 fera, Ilex verticillata, Rhamnus alnifolia, Chamaedaphne caly- 

 culata, Pyrus arbutifolia, Salix lucida, Salix Candida, Benzoin 

 aestivale, Ruhus hispidus, Aster puniceus, Sphagnum, Ranun- 

 culus septentrionalis, Caltha palustris, Aspidium Thelypteris, 

 Aspidium cristatum, Osmunda cinnarnomea, Osmunda regalis, 

 Onoclea sensihilis, Symplocarpus foetidus, Veratrum viride, Viola 

 cucullata, Ranunculus, recurvatus, etc. 



The species which occur in the depressions are most variable, 

 since they are subjected to the greatest variation in conditions 

 of environment. Frequently Alnus incana forms dense stands 

 occupying large areas, and when present usually dominates. It 

 is especially characteristic of swamps which are traversed by 

 small streams, or of undrained areas upon relatively unstable 

 humus. Its most common position is the low boggy humus on 

 either side of swamp streams where it differs from the other 

 members of the shrub stage in that it is not necessarily associated 

 with hummocks. 



This cool wet situation is somewhat different from the more 

 removed portion of the swamp for there is a greater circulation 

 of the soil water, and hence a lower acidity. There are associ- 

 ated with this habitat a few forms which are relatively uncommon 

 outside this situation, namely ; — Cardamine pennsylvanica, Helen- 

 ium autumnale, Sium cicutaefolium, Polemonium reptans, etc. 



The Forest Stage 



Deciduous Swamp Forest. Previous to the establishment of 

 the swamp forest there may be considerable instability of the 

 soil. This is due to its being built up from a depth of several 

 feet by the accumulation of a loose humus which has undergone 

 only partial decomposition ; and because of its texture and high 

 water holding capacity. Because of this origin the mucky sub- 

 stratum is frequently found to quake in the various stages up 



