196 PLANT LIFE. 



becomes very quickly covered over by the Alga, 

 Vaucheria (alluded to above, p. 181). It forms a tough 

 and flexible carpet, well adapted to fix the loose soil, 

 and has a beautiful velvety dark-green colour. There 

 are many marine worms and other creatures in these 

 Vaucheria cushions. The estuarine Chenopodiaceae, and 

 especially Salicornia herbatea^ should be looked for 

 about or a little below this level. Below this again 

 is the habitat of Ruppia, and, still lower, of Zostera. 



The formation of small creeks is very common in 

 mud-flats. Fresh- water streams also cut out little 

 deltas or deep channels. Sometimes also the banks 

 of a tidal river will slope downwards, away from the 

 stream, forming miniature lagoons or marshy places. 

 The tide enters all these depressions, and it is in them 

 that Reeds appear to flourish. These are to be found 

 in bays partly sheltered from the scour of the current, 

 and with a depth of perhaps 6-12 inches of water at 

 high tide. The dominant plant of these reed beds upon 

 the Clyde is Scirpiis lacustris var. Tabernaejnontani; 

 it gives off horizontal runners about nine inches long, 

 which fix themselves firmly in the mud by several 

 roots. Each fixed point is a new base for the produc- 

 tion of fresh runners and foliage branches. In such a 

 bed, between forty and fifty vertical stems may be 

 counted upon a square foot of soil. As the leaves 

 wither and die, they are entangled amongst the vertical 

 stalks, which last through the winter in a withered 

 condition. Anything floating in the water, such as 

 cotton rags, dead leaves, silt, and refuse of all kinds, 

 becomes entangled, and is retained amongst the stems. 

 Ectocarpus crinitus and other Algae also develop between 

 them. Hence the level of the soil gradually rises ; and 

 very soon the landward side begins to be peopled by 



