1912] SHERFF—SKOKIE MARSH 419 
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 appreciable extent in these two associa- 
tions, the 10 most abundant (Sium, Polygonum hydropiperoides, 
P. Muhlenbergii, Nymphaea, Castalia, Rumex, Veronica, Myrio- 
phyllum, Callitriche palustris, and C. heterophylla) are dicotyledons.*® 
In the other thfee associations the most abundant species are 
chiefly monocotyledons. 
The swamp meadow differs from the reed swamp in being more 
uniform, due to greater parallelism between the water table and the 
soil surface, and does not admit of logical subdivision into associa- 
tions. The plants are principally such grasses as Calamagrostis 
canadensis, Glyceria nervata, Phalaris arundinacea, Poa triflora, 
Sphenopholis pallens, and Agrostis perennans. These are fre- 
quently interspersed with Carex lupuliformis, C. vesicaria monile, 
Scirpus atrovirens, and S. Eriophorum. 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 late autumn. 
Most of the shrubs and young trees are killed in this way, and so 
forest development is hindered. Trees occur only in small groups, 
consisting chiefly of Salix (S. nigra and other species), Fraxinus 
americana, and Populus tremuloides. Frequently associated with 
these are such shrubs as Cornus stolonifera, Cephalanthus occiden- 
talis, and Sambucus canadensis. 
Throughout the reed swamp and swamp meadow are many 
species which, though very abundant, share only to a small extent 
in giving to the several associations their distinctive appearance. 
Thus, Ludwigia palustris, Proserpinaca palustris, Penthorum 
sedoides, and Stenophyllus capillaris are low in habit and obscured 
by taller plants in the shade of which they may thrive. Again, 
Aster Tradescanti, Boltonia asteroides, Lobelia cardinalis, Teucrium 
occidentale, and Scutellaria galericulata, while extremely common, 
are nevertheless conspicuous only during the latter part of the 
summer. The names of such species will be given in this paper only 
where occasion demands. 
5 See HENSLow — — regarding the supposed monocotyledonous nature 
of Nymphaea and Castal. 
