386 Annals of the Carnegie Museum. 



The Scirpiis Formation. 

 The Scirpus formation is here much more extensive than in the 

 habitat just referred to. It has a maximum width of perhaps one- 

 third of a mile, and in places forms a quite dense growth, which quite 

 effectually calms the waves of ordinary storms. Zonatipn within the 

 formation is clearly evident in the deeper zone (consocies), charac- 

 terized by Scirpus validus, and in the shallower zone characterized by 

 Scirpus americanus. There are a very few isolated families of Ponte- 

 deria cordata and Sagittaria rigida mainly in the Scirpus validus 

 consocies. 



The Phragmites-Typha Marsh Formation. 



The shallower part of the habitat, occupied in the earlier stage by 

 Scirpus americanus, has now been taken over by a well marked forma- 

 tion with the following structure : 



Fades. — 



Phragmites phragmites, Typha latifolia. 



Principal Species. — 



Zizania aquatica. 



Secondary Species. — 



Sagittaria latifolia, Spargafiium eurycarpum, 



PcT'sicaria laurina, Jtmctis ca?iadensis. 



This formation, as compared with the Scirpus- Typha formation of 

 the ponds and' lagoons at the northern end of the peninsula, presents 

 some interesting differences. In the lagoons Scirpus validus, although 

 occupying the deeper part of the habitat, never occurs in so deep 

 water as it occupies in the bay, and it usually alternates in the ponds 

 with Typha latifolia. With the Typha, however, the case is different. 

 It occupies about the same depth of water as in the ponds and lagoons, 

 rarely more than fifteen to eighteen inches deep. This may be due, 

 perhaps, to the inability of the Typha to cope with the surf in the bay. 



The formation exhibits one marked aspect characterized by Zizania 

 aquatica, this society filling in the areas not occupied by the Phrag- 

 ynites and Typha consocies, and, during the latter half of the season, 

 largely obscuring the associated secondary species. 



The Phragmites-Typha formation is characterized, in a general way, 

 by the ])Ossession of large rootstocks and the production of a rather 

 large amount of aerial and submerged vegetation, which each season 

 adds materially to the humic content of the soil, thus producing in a 



