i88 HELOPHYTES sect, v 



Alisma Plantago, Sagittaria, Sparganium ramosum, S. simplex, Acorus 

 Calamus, and Calla palustris, which together represent the most important 

 monocotylous representatives of this oecological class in temperate 

 Europe ; to these may be added Equisetum hmosum, and, among Dicoty- 

 ledones, Senecio paludosus, Sonchus palustris, Menyanthes trifoliata, 

 Lythrum Sahcaria, Epilobium hirsutum, Rumex Hydrolapathum, Lysima- 

 chia vulgaris, L. thyrsiflora, Ranunculus Lingua, Oenanthe fistulosa, 

 O. aquatica. Slum latifohum, S. angustifohum, Cicuta virosa, and many 

 others. Many diatoms and Green Algae occur as epiphytes. 



Especially on the banks of water-stretches is found this vegetation, 

 which advances as a pioneer of land-vegetation, acts as a check to wave 

 violence, and adds to the land.^ 



According to depth of water and other conditions dependent thereon 

 (light, temperature, and water-movement) this formation is hkewise 

 arranged in zones, which in Denmark and over the greater part of Europe 

 are identical, and may be pure associations, such as phragmiteta, scirpeta, 

 and so forth. Magnin '^ and Schroter ^ have observed, in Lakes Jura 

 and Constance respectively, the following zones : scirpeta (Scirpus 

 lacustris down to 3-5 metres in Lake Constance), phragmiteta (Phrag- 

 mites communis down to 2 metres), after which succeed heleochareta 

 (Heleocharis palustris), and cariceta (in Denmark, C. aquatilis, C. rostrata, 

 and others). All these plant-communities work in the direction of filhng 

 up collections of water and draining them dry. There also occur typheta, 

 equiseteta, and others. 



Precisely the same zones present themselves in North Europe and 

 North America. According to Transeau,* in the Lakes of Michigan, after 

 the aquatic societies containing Potamogeton and Nymphaea, there 

 succeeds the ' cat-tail-DuHchium association ' with Typha, Phragmites, 

 and Dulichium. Further inland follow the ' Cassandra society ', ' shrub- 

 and-young-tree ' association, and forest. Cowles ^ finds in the vicinity of 

 Chicago the following zones : (i) Chara ; (2) Nymphaea ; (3) Carex and 

 Scirpus ; (4) Cassandra calyculata and other shrubs ; (5) Forest. In 

 other places the cariceta are succeeded by grass meadows.^ 



Adaptations. Vigorous creeping stems fasten the plants to the loose 

 soil, causing social growth and dense pure associations of Phragmites, 

 Scirpus lacustris, Equisetum limosum, Typha, and many others; also, 

 on the Nile, Cyperus Papyrus. The production of shoots by roots, 

 which is so frequent in dry spots, rarely occurs in the vegetation of reed- 

 swamps, but is exhibited by Sium latifolium. Caespitose species are 

 likewise rare. 



The vegetative shoots vary in construction, but mainly belong to one 

 of three types : 



(a) Leafless, bare stem consisting of one internode, which may be 

 either one or two metres in length, and is capped by the inflorescence ; 

 as examples, we may mention Scirpus lacustris, S. Tabernaemontani, which 

 are as much as 1-2 metres in height, also Heleocharis palustris and 

 species of J uncus which are shorter. 



' See Section XVI. " Magnin, 1893, 1894. 



^ Schroter und Kirchner, 1896-1902. * Transeau, 1903, 1905. * Cowles, 1901. 

 * See also Pieters, 1894, 1901 ; Hitchcock, 1898 ; V. Borbas (Bernatsky), 

 1907 ; Friih und Schroter, 1904. 



II 



