589 



shoots of Polygonum rise above those of Aconis and Galium with- 

 out apparent harm to either of them. And while Polygonum might 

 increase in abundance if Acorns and Galinni were entirely absent, 

 still to a great extent the community, viewed as a whole, is comple- 

 mentary. Elsewhere in the Irido-acoretum the rhizomes of Aconis 

 are replaced by those of Iris; and very often the rhizomes of Galium 

 are replaced by those of Ludvigia palustris, L. polycarpa, Proser- 

 pinaca palustris, Pentlwrum sedoides, Veronica scutcllata, or Cam- 

 pan 'tla 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 

 Mnhlenbcrgii 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 in- 

 carnafa and Sium cicutaefolium, which root near the surface, may 

 reproduce largely by seed or by new shoots arising from the old 

 stem base of the preceding year. In the middle and latter parts of 

 the summer, when the surface soil is no longer saturated with water, 

 such annuals as Panicum capillarc, Bcliinochloa crusgalli, Erar/rostis 

 hypnoidcs, Stenophylhis capillaris, Polygonum Persicaria, Acnida sp. 

 (see Annotated List, No. 89), Amaranthns paniculatus, and Brechtites 

 hicracifolia take possession of all exposed surface soil and become ex- 

 ceedingly abundant. ]\Iuch of the surface soil that has been denuded 

 by burning or by other causes is already occupied, however, by the 

 rhizomes of perennials such as Ludvigia palustris, L. polycarpa, 

 Proserpinaca palustris, etc. In these cases Boltonia astcroides, Cal- 

 litrichc licterophyJla, and C. palustris are often abundant. Both spe- 

 cies of Callitriche, however, die away in midsummer, being replaced 

 by annuals. Figure 11, Plate XCI, shows such a community. Calli- 

 triche, maturing earliest, is "seasonally" (Woodhead '06) comple- 

 mentary with the other species. Boltonia roots lowest, while its 

 aerial shoot grows much the highest ; and since it is not harmed 

 \'er}- much by Proserpinaca, Liidrigia, and Pentlwrum, while they 

 derive, if anything, benefit from its shelter, Boltonia is complementary 

 both aerially and subaerially. Proserpinaca, Ludzigia, and Pentlw- 

 rum are very similar throughout in growth form and they consti- 

 tute mutually a competitive community; but, even though mutually 

 competitive, they form with Boltonia and Callitriche a community 

 that may properly be called complementary. 



