1912] SHERFF—SKOKIE MARSH 429 
they in turn do little harm to it. In late summer, the shoots of 
Polygonum rise above those of Acorus and Galium without apparent 
harm to either of them. And while Polygonum might increase in 
- abundance if Acorus and Galium were entirely absent, still to a 
great extent the community, viewed as a whole, is complementary. 
Elsewhere in the Irido-acoretum the rhizomes of Acorus are replaced 
by those of Jris; and very often the rhizomes of Galium are re- 
placed by those of Ludwigia palustris, L. polycarpa, Proserpinaca 
NE 
| i 
" ¥ 
“ A 
RO AZ AIP Se = : 
Fic. 7.—a, Acorus Calamus; b, Polygonum Muhlenbergii; c, Galium Claytoni; July 
palustris, Penthorum sedoides, Veronica scutellata, or Campanula 
aparinoides. 
The basal parts of the various swamp meadow species are 
usually more slender than those of the reed swamp species, and 
hence the texture of the surface mat of rhizomes, roots, etc., is 
finer. Then, too, reproduction by seeds becomes more common. 
Polygonum Muhlenbergii is present in the swamp meadow, and by 
means of its extensively creeping rhizomes, which lie rather low, 
it forms in some places large patches. Certain other perennials, 
e.g., Asclepias incarnata and Sium cicutaefolium, which root near 
the surface, may reproduce largely by seed or by new shoots aris- 
ing from the old stem base of the preceding year. In the middle 
