68 LAND-FORMING PLANTS. 



Similar transitional belts exist to every community of plants. 

 Thus, for example, there is a fringe of special species between 

 the bare earth of a road and the grass by the footpath. At 

 the edge of every railway track, on every ballast-heap, on every 

 bare exposed rock, in the shingles and sandbeds of rivers, in fact 

 wherever a dominant plant-association is interrupted by any cause, 

 there we find a distinct and definite series of fringing species. 



Plants which assist to form culture-land are extremely numerous. 

 In this country, besides the water species, there are fringes to the 

 sand-dunes on which Psamma is at first the only species, as well 

 as fringes to rocks and walls, to ballast-heaps, etc. Warming gives 

 a large number of other cases, such as those found on lava plains, 

 rock-slips, rock-falls, burnt wood, or burnt meadows, abandoned 

 cultivation, etc. The subject covers far too wide a ground there- 

 fore for one paper, and I have restricted myself entirely to the 

 land-acquiring plants of fresh or brackish water. 



A very good example of a land-forming plant is Scirpus lacuslris 

 var. Tabernamontani, which occupies a considerable number of 

 the bays about Langbank wherever a suitable muddy floor is 

 present. The plant has horizontal skirmishing runners which fix 

 themselves by long roots about 9 inches apart. This, or a little 

 less, may be taken as the annual advance towards the water. 

 Once established, about 40 to 50 vertical dead stems may be 

 counted in an area of a square foot. Dead leaves and floating 

 rubbish of all kinds, old rags, corks, floating stems of the plant 

 itself, catch amongst these vertical leaves. It is, in fact, a sort of 

 honeycomb of dead Scirpus leaves, vertical stems and leaf bases 

 forming a kind of stake-and-bind arrangement, and silt will 

 accumulate in it until the level rises year by year above ordinary 

 tides. This process is much assisted by the growth and decay of 

 Ectocarpus crinitus, Vaucheriae, Diatoms, and other attached algae; 

 the whole forms a tangled mass of decaying organic matter, and 

 gradually raises the soil. 



Examining the landward side of such a bed, the first plants to 

 make their appearance are Cochlearia officinalis, Aster Tripolium, 

 Armeria, Juncus acutiflorus and Agrostis alba. Then a few Iris 

 rhizomes, afterwards Juncus communis, and finally the meadow 

 grasses appear ; the last are regularly grazed by cattle. Of these, 

 all have peculiarly sturdy stems and considerable staying power 



