VEGETATION OF THE MARSH AND BOG 243 



latter is often quite aquatic in habit, with finely-cut 

 submerged leaves and broader floating ones Sium lati- 

 folium and 8. angustifolium (water-parsnips), Scrophu- 

 laria aquatica (marsh-fig wort), Veronica scutellata (marsh- 

 speedwell), V. Beccabunga (brooklime), V. Anagallis 

 (water-speedwell), Mentha aquatica (water-mint), Poly- 

 gonum amphibium, P. Hydropiper, Eumex Hydrolapa- 

 thum (great water-dock). 



The reed-swamp may be succeeded on its landward 

 side by true marsh or woodland-swamp, or damp meadows 

 may extend almost to the water's edge. In the latter case, 

 and also when a towing-path is present, the river-bank 

 is occupied by a mixed assemblage of plants, dominated 

 by sedges, grasses, and rushes. The roots or rhizomes of 

 these plants are usually situated in saturated soil, but 

 no part of the assimilating organs is under water. It is 

 here that the annual marsh-plant finds a home (see list, 

 p. 241). The most frequent perennials are : Thalictrum 

 flavum (meadow-rue), Althcea offlcinalis (marsh-mallow), 

 Spircea Ulmaria (meadow-sweet), Lythrum Salicaria 

 (purple loosestrife), several species of Epilobium (willow- 

 herbs) and Mentha (mints), Valeriana offlcinalis, Eupatorium 

 cannabinum (hemp-agrimony), Senecio aquaticus (marsh- 

 ragwort), Lysimachia vulgaris (yellow loosestrife), Lycopus 

 europceus (gipsy-wort), Scutellaria galericulata (skull-cap), 

 Stachys palustris (marsh-woundwort), Myosotis palustris 

 (marsh forget-me-not), Symphytum officinale (comfrey), 

 and isolated trees of willow, alder, and birch. 



The dominant plants of the reed-swamp possess sub- 

 terranean creeping stems which tend to travel away from 

 land. Humus collects at the base of the plants, and in 

 lakes and ponds the bottom, through its accumulation, 

 gradually rises. In this way a pond may be choked up 

 and converted into a marsh. The danger is not so great 

 in rivers, for the humus is carried away by the current, 

 but even here the plants must be periodically removed 

 to keep the water-way clear. 



2. Woodland or Bush-Swamp. 



The alder and willow, which are usually found sparingly 

 in the reed-swamps, may become very numerous and 

 form distinct associations along the margins of rivers ; 

 or they may extend for a considerable distance landwards 



