102 J. E. CRIBBS 



formation for a long period of time. This phase in development 

 is commonly referable to one of three causes: (1) Because of 

 frequent burning. Burning strongly inhibits the development 

 of many shrub and tree species. (2) Partial Submergence. This 

 follows the melting of winter snows and the occurrence of heavy 

 spring rains. (3) Raising of the water table. This is commonly 

 caused by the seepage of water from adjacent regions, or by the 

 presence of springs. It is especially the latter two of these 

 conditions which are responsible for the retention of the open 

 swamp phase. 



A very noticable feature of these stages is the development of 

 two types of vegetation; one characteristic of the spring and 

 early summer, and the other of late summer and autumn. The 

 vernal and early summer type is composed primarily of aero- 

 aquatics and species adapted to growing in low muddy or marshy 

 situations. This is made necessary by the great abundance of 

 water present over the area during this season. In the compo- 

 sition of this vegetation there are a number of species which 

 may be considered typical, but as in all plant associations, they 

 vary in different localities, chiefly because of local limits to 

 migration. Among the most representative of the species may 

 be mentioned, Typha latifolia, Scirpus americana, Caltha palus- 

 tris, Senecio aureus, Polymonium reptans, Polygonum amphibium, 

 Polygonum Hydropiper, Symplocarpus foetidus, Aspidium The- 

 lypteris, Onoclea sensibilis, Sphagnum, Cicuta bulbifera. Ranun- 

 culus septentrionalis, Veratrum viride, Viola cucullata, Saxi- 

 fraga pennsylvanica, etc. 



Later in the summer the habitat may be greatly changed by 

 the evaporation and gradual drainage of the surplus water, so 

 that the water table is lowered and conditions become much 

 more xerophytic. The relative abundance of vegetation is 

 greatly reduced; and that which remains is, because of its 

 greater openness, subject to very desiccatmg influences such as 

 intense heat and light exposure associated with a low water 

 content in the soil. These in conjunction with the acidity and 

 low soil temperature initiate the changes in floral composition. 



The autumn flora is usually strongly represented by the rushes 



