TYPICAL SWAMP AREAS. 53 
the water's edge by the Scirpus. Scirpus lacustris is also 
present here, but remains secondary in importance to S. 
maritimus. Sagittaria variabilis follows along the shore in 
patches. Bidens frondosa begins in this zone but culmin- 
ates on the shore side. Diminutive forms, Wolffia, Lemna 
and Spirodela, are found abundantly in this zone. The 
second zone varies greatly in width and the tension line 
between it and the first is very irregular. 
The Carices are the most abundant forms, but not so 
conspicuous as some larger plants which are equally com- 
mon with each other. This association consists of Poly- 
gonum Muhlenbergii, Boehmeria cylindrica, Apocynum 
androsaemifolium, Hibiscus militaris, Amorpha fruticosa 
and Bidens frondosa. Pilea pumila is very abundant but 
not conspicuous. Bordering this zone, there isa slight rise 
of six inches or more which is sufficient to introduce a 
shrub or tree margin, and along this border line Amsonia 
Tabernaemontana, Cephalanthus occidentalis and Salix lon- 
gifolia are prominent. (Plate 9.) In the shrub zone one 
notes a few climbing forms, Polygonum scandens, Apios 
tuberosa and Strophostyles palustris. Eupatorium coeles- 
tinum is most common, E. altissimum and Erigeron annuus 
are secondary, while Salix amygdaloides and Betula lutea 
are the most characteristic shrubs. This zone gradually 
merges into the real tree zone which occupies the old 
river shore. Immense sycamores (Platanus occidentalis), 
swamp maples (Acer rubrum) and cottonwoods (Populus 
monilifera) are the typical trees. A dense undergrowth of 
shrubs is found here, the most noticeable of which are 
Betula lutea, Salix amygdaloides, Forestiera acuminata, 
Ulmus fulva, Fraxinus Americana, Crataegus viridis, Cor- 
nus asperifolia and Gleditsia triacanthos. Sicyos angulata, 
Vitis cinerea, V. riparia and Tecoma radicans are the prom- 
inent lianas. Boehmeria cylindrica, Astragalus Canadensis 
and Oenothera biennis are common and in small clearings 
Ambrosia trifida and A. artemisiaefolia have been introduced. 
