418 BOTANICAL GAZETTE [MAY 
the girdles of Nymphaea and Castalia are peculiar to them and 
justify their treatment as a separate association, the Vymphacetum. 
Landward from the Nymphaeetum are found dense and either 
intermixed or almost pure growths of Typha latifolia, Sparganium 
eurycarpum, Scirpus ‘fluviatilis, and S. validus. Scattered to a 
varying extent among these species are Sagittaria latifolia and Sium 
cicutaefolium. Were and there are a few isolated patches of 
Dulichium arundinaceum and of Decodon verticillatus. This 
* 
Fic. 3.—Skokie Stream at point west of Glencoe, looking south; July 
association will be referred to as the Scirpo-typhetum. Then 
again, in certain parts of the reed swamp, at stations slightly less 
hydrophytic, Phragmites communis is prominent. It forms exceed- 
ingly compact, nearly pure colonies that may reasonably be treated 
as an association, the Phragmitetum. Finally, we must mention 
the many large but somewhat scattered patches of Iris versicolor 
and Acorus Calamus, occurring in the outer parts of the reed.swamp 
and often extending into the swamp meadow formation. These con- 
stitute an association of a very definite stamp, the Iridoacoretum. 
