105] TRANSEAU—BOGS OF THE HURON RIVER VALLEY 433 
Nymphaea advena is of great importance. It forms an almost con- 
tinuous zone 10 to 25 fect (3-7.5 ™) in width. Patches of Castalia 
tiberosa and Brasenia purpurea occur. This arrangement in groups 
sems 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 societ'y.—Carex fili- 
formis, C. oligosperma, Eleocharis 
palustris glaucescens, and Erio- 
phorum polystachyon are the pri- 
mary factors in the formation of 
thiszone. Carex riparia has gained 
afoothold at the north end of the 
like, where muskrats have been 
active in destroying the original 
sedge zone. Dryopteris thelypteris, 
Onoclea sensibilis, Juncus effusus, 
J. canadensis, Comarum palustre, 
“x myrtilloides, Dulichium arun- 
dinaceum, Equisetum _ fluviatile, 
Bidens trichosperma tenuiloba, ' eat 
Menyanthes trif oliata, Viola Fic. 6.—First Sister Lake. 
/ blanda, and Eriophorum virgini- 
(“tm occur as accessory plants. The great majority of these suns 
a 2 the construction of the substratum by their roots and root- 
Here and there among the sedges occur the forerunners of the 
b society. Among the very first to gain a foothold are the 
‘phagnums. These build small tufts of great compactness and 
Stadually overcome the sedges. The rootstocks of the cassandra 
send up shoots and prepare the way for another vegetation a 
Oxycoccus macrocarpus and O. Oxycoccus both occur at intervals 
i this zone. 
Cassandra-sphagnum sociely.—Beyond th 
Hon is no longer arranged zonally. Conditions 
e sedge zone the vegeta- 
have been so muc 
