SEAWEEDS AND THE WATER-FLORA. 1 97 



Other forms. First, the mud plants, such as an odd 

 specimen of Coclilearia, of Aster Tripoliuin^ of Agrostis 

 alba, or a few plants of Iris, and, finally, the common 

 Rush and the regular meadow grasses. 



Several other Cyperaceae act somewhat in the same 

 manner, but they are not of so much importance. 

 Scirpus riifus has a particularly neat system of horizon- 

 tally creeping runners extending seawards. Both this 

 and 6". lacustris, as well as the fresh-water reeds, 

 obviously render the soil unsuitable for themselves by 

 their own growth, and they are essentially pioneers 

 preparing or " winning " new land for the ordinary 

 grasses. In all estuarine and alluvial land, vegetation 

 of this kind has played a very important part in 

 physical geography, although it seems to have escaped 

 the notice of most geographers. It is upon such 

 alluvial flats that the greatest part of the world's 

 population is maintained, as is easily seen by referring 

 to such cases as the Rhine, the Thames, the Yangtse- 

 kiang, the Nile, the Ganges, and the Clyde. Surely, 

 therefore, these estuarine plants deserve a more thorough 

 examination than they have yet received. 



