110 J. E. CRIBBS 



spring rains and the melting of winter snows. Hence it makes 

 possible the more rapid succession. The hmnus becomes com- 

 pact at an earlier stage than in the preceeding series; evidently 

 due to the more uniform water table, and the more complete 

 disintegration of organic matter. 



The Aquatics 



The aquatic stages in this sequence bear a close resemblance 

 to those of the swamp series, and it will suffice in discussing 

 them here to merely allude to some of the differences which may 

 occur. 



Among the submersed aquatics there are a number which 

 develop in greater abundance in the lake successions than in the 

 swamp series. This is especially true of those which are in- 

 hibited by the presence of acid in the water. Of these Nitella 

 is perhaps the most conspicuous. 



In the aero-aquatic and marsh zones there are found some 

 differences. In addition to the species already enumerated as 

 characteristic of this position in the former series, there occur 

 a few additional ones which are more strictly limited to fresh 

 water ponds and lakes. Among these are Pontederia cordata, 

 Sagittaria latifolia, Iris versicolor, Sparganium eurycarpum, 

 Eleocharis olivacea, Cicuta maculata, and Castalia odorata. 



The Fen 



One of the essential differences in the swamp and lake-forest 

 series occurs in the appearance of a fen instead of an open-swamp 

 stage. The land lies low but is quite firm and is not, as in the 

 latter instance, characterized by the formation of hummocks. 

 The transition from the marsh to the fen is usually gradual and 

 is a change from a rush to a sedge stage. 



The flora is typically low and herbaceous, and consists es- 

 sentially of Lycopus americanus, Lycopus virginicus, Ly thrum 

 alatum, Scirpus americanus, Bcehmeria cylindrica, Radicula 

 palustris, Carex cristata, Carex scirpoides, Carex stricta, Carex 

 crinita, Carex flava, Carex aurea, Verbena hastata, Eupatorium 



