577 



Generai, Features oe the Marsh Vegetation 



Upon analysis, the vegetation at Skokie Marsh is found to con- 

 sist of three rather pronounced formations.'^ Along the course taken 

 by Skokie Stream, the plants constitute distinctly a reed swamp 

 formation (PI. LXXXVII, Fig. 2). Extending along on either side 

 of the reed swamp is a broad level expanse, intermediate between 

 reed swamp and meadow. This mav be designated swamp meadow 

 (PI. LXXXVII, Fig. 3; PI. XCIV, Fig. 18; PI. XCV, Fig. 19). At 

 the outer edges of the swamp meadow, in narrow areas that have not 

 been too much disturbed by cultivation, true meadow is commonly 

 present. At certain places, however, there is an abrupt transition 

 from swamp meadow, or even from reed swamp, to forest. Such a 

 case is shown admirably in Plate XCV, Fig. 20, which pictures a 

 small piece of forest containing Querciis rubra, Q. macrocarpa, Q. 

 alba, Jiiglans nigra, etc., separated from a branch of the reed swamp 

 by a distance of only about 15 m. 



In the reed swamp the plants belong to five easily recognized as- 

 sociations. Where the stream is deepest (as in PI. LXXXVII, Fig. 2), 

 aquatic or amphibious species, such as Myriophyllum humile,-\ M. 

 licterophyllmn, Ranunculus dclpliinif alius, and Potainogcton (/:os- 

 terif alius?) are common near the center. In the shallower parts, 

 the species are supplemented or replaced by Polygonum Muhlcnbergii, 

 P. hydro piperoides, V^eronica Anagallis-aquatica, Radicula aquMtica, 

 Sium cicutaefoliuui, Sparganiuui eurycarpum, Glyceria septentrio- 

 nalis, Alisnia Plantago-aquatica, Runiex vcrticillatus, CallifricJie het- 

 crophylla, and C. palustris. As Polygomiui hydropipcroidcs and Sium 

 cicutae folium are among the most abundant stream plants and ap- 

 pear to be dominant, we may classify the plants growing in the 

 stream or upon its bed, except along the margins, as the Siuui-Polyg- 

 onum association; or, using Schouw's method of nomenclature 

 (Schouw, '22, pp. 148-150), we shall call this the Sio-polygonetuui 

 On either side of the Sio-polygonetum a narrow or sometimes broad 

 girdle^ of Nymphaea advcna and Castalia odorata occurs in many 



*The words "formation" and "association" are used throughout this paper in 

 the sense accepted by Warming ('09, pp. 140, 144). 



tAll plant names given in this paper conform, unless otherwise noted, with the 

 nomenclature of Gray's Manual (see Robinson and Fernald, '08). 



jThe word "girdle" is here equivalent to the "zones" of many recent authors, 

 and conforms with the recent proposal of Flahault and Schroter ('10), except that 

 it is here used for "bands" that are not "concentric." Professor Schroter kindly 

 informs me by letter that this use of their word is perfectly justifiahle, and further 

 says, "we should have made provision for such a use." 



