&\l : THE 'BOOK OF NATURE STUDY 



particularly high, and the channel bed is formed of soft, muddy 

 materials. The vegetation is xerophytic in character, for a 

 muddy salt marsh has great extremes of heat and cold, of moisture 

 and dryness. The plants are characterised by a low growth, 

 a comparatively undeveloped root-system, and fleshy leaves ; or 

 by fleshy stems bearing leaves very much reduced in size. At each 

 high tide the waters of such a shallow channel as the Bristol 

 Channel lay down a considerable thickness of mud ; thus the 

 formation of a muddy salt marsh begins. Soon there will be 

 a layer of mud, washed by all high tides. Here the Glasswort 

 (Salicornia herbacea) establishes itself ; often it is the only 

 species found. The accompanying photograph shows the plants 

 some distance apart, not competing in any way with each other. 

 A few green seaweeds may be found in this belt, and sometimes 

 the Suceda maritima. When the Glasswort grows thickly it 

 covers the mud-flats with a sheet of vivid green, which changes 

 to brown in autumn ; of all the plants growing in salt marshes, 

 it is the one that creeps farthest down to the sea ; the first belt 

 or zone of vegetation in these muddy shores is therefore that of 

 the Salicornia herbacea. The plant has short, thick leaves, and a 

 stem, succulent above, which bears branches given off in pairs at 

 each node, and these again branch, each ending in a spike. The 

 flowers are very minute, with a green perianth, one or two 

 stamens and two styles projecting from the perianth. The 

 Suceda maritima belongs to the Goosefoot family, and is a low- 

 growing plant, sometimes only two or three inches high. It has 

 small, linear, succulent leaves and small, green flowers, two or 

 three together in the axils of the leaves. It forms a sub- 

 dominant species. 



Behind the Salicornia belt, another Plant Association, that of 

 the grass, Glyceria maritima, establishes itself. Here the mud bank 

 is rather higher and the ground is washed by spring tides only in 

 time of storms. This situation is therefore drier than the last. 

 The two plants most usually found with this grass on the shore in 

 question are the Sea Starwort (Aster Tripolium) and the Sea Arrow- 

 grass (Triglochin maritimum). The Sea Aster is distinguishable 

 from all other British Composites by its large flower heads, with 

 a yellow disc and purple ray. It is seldom more than a foot high. 



