1905] TRANSEAUBOGS OF THE HURON RIVER VALLEY 433 



Nymphaea advena is of great importance. It forms an almost con- 

 tinuous zone 10 to 25 feet (3-7.5 m ) in width. Patches of Castalia 

 tuberosa and Brasenia purpurea occur. This arrangement in groups 

 seems to be connected with their rapid multiplication by rhizomes. 

 Typha latifolia occurs in a small area at the north end of the lake. 

 Ceratophyllum demersum and 

 Naias flexilis occur as secondary 



species. 



Bog-sedge society. Carex fili- 

 formiSj C. oligosperma, Eleocharis 

 palustris glaucescens, and Erio- 

 phorum polystachyon are the pri- 

 mary factors in the formation of 

 this zone. Carex riparia has gained 

 a foothold at the north end of the 

 lake, where muskrats have been 

 active in destroying the original 

 sedge zone. Dryopteris thelypteris, 

 Onoclea sensibilis, Juncus effusus, 

 J. canadensis, Comarum palustre, 

 Salix myrtilloides, Dulichium arun- 

 dinaceum, Equisetum fluviatile, 

 Bidens trichosperma tenuiloba, 

 Menyanthes trifoliata,Viola 

 blanda, and Eriophorum virgini- 



cum occur as accessory plants. The great majority of these plants 

 aid in the construction of the substratum by their roots and root- 

 stocks. 



Here and there among the sedges occur the forerunners of the 

 shrub society. Among the very first to gain a foothold are the 

 sphagnums. These build small tufts of great compactness, and 

 gradually overcome the sedges. The rootstocks of the cassandra 

 also send up shoots and prepare the way for another vegetation form. 

 Oxycoccus macrocarpus and O. Oxycoccus both occur at intervals 

 in this zone. 



Cassandra-sphagnum society. Beyond the sedge zone the vegeta- 

 tion is no longer arranged zonally. Conditions have been so much 



Scale. 



FIG. 6. First Sister Lake. 



