578 



places along the stream. Usually these species are accompanied by 

 species characteristic of the Sio-polygonetum ; but the soil and light 

 conditions present in the girdles of Nyniphaca and Castalia are pecu- 

 liar to them and justify their treatment as a separate association, the 

 Nyniphacetuiii. Landward from the Nymphaeetum are found dense 

 and either intermixed or almost pure growths of Typha latifolia, 

 Sparganium cnrycarpuni, Scirpus fluviatilis, and S. validus. Scat- 

 tered to a varying extent among these species are Sagittaria latifolia 

 and Slum cicutaefolium. Here and there are a few isolated patches 

 of Dulichiuni arundinaceum, of Decodon verticillatuSj and of certain 

 other species. This association will be referred to as the Scirpo- 

 typhetuiu. Again, in certain parts of the reed swamp, at stations 

 slightly less hydrophytic, Phragiuitcs communis is prominent. It 

 forms exceedingly compact, nearly pure colonies that may reasonably 

 be treated as an association, the Phraginitetnin. Finally, we must 

 mention the many large but somewhat scattered patches of Iris ver- 

 sicolor and Acorns Calamus, occurring in the outer parts of the reed 

 swamp and often extending into the swamp meadow formation. These 

 constitute an association of a very definite stamp, the /ndo-acorefwm. 

 A general comparison of the reed swamp associations shows that in 

 the Sio-polygonetum and Nymphaeetum, where hydrophytism is 

 greatest, the dominant plants are dicotyledonous. In fact, of the 15 

 species found to any considerable extent in these two associations, 

 the 10 most abundant (Sium cicutaefolium, Polygonum hydropiper- 

 oides, P. Mnhlenbergii, Nympliaea advena, Castalia odorata, Rnmex 

 vcrticillatus , Veronica Anagallis-aqiiatica, Myriophyllum humile,* 

 CallitricJie palustris, and C. heterophylla) are dicotyledons. f In the 

 other three associations the most abundant species are chiefly mono- 

 cotyledons. 



The swamp meadow differs from the reed swamp in being more 

 uniform, owing to greater parallelism between the water-table and the 

 soil surface, and does not admit of logical subdivision into associations. 

 The plants are principally such grasses as Cala)}iagrostis canadensis, 

 Glyceria ncn'ata, Piialaris arundinacea, Poa triflora, Sphenopholis 

 pollens, and Agrostis perennans. These are frequently interspersed 

 with Carex lupuliformis, C. vesicaria monile, C. riparia, Scirpus 

 atrovirens, S. Briophorum, etc. The swamp meadow is used by 

 farmers of the district for the production of marsh hay, and many 

 of them customarily burn over the areas in the late autumn. Most 

 of the shrubs and young trees are killed in this way, and so forest 



*But see Nos. 136 and 137 in Annotated List. 



tSee Henslow ('11). however, regarding the supposed monocotyledonous na- 

 ture of Nymphaea and Castalia. 



