128 SUCCESSION 



in the case of bad lands, or, more frequently, they are 

 mesotropic, passing first through a long series of xerophytic 

 formations. Sandbars (cheradia, syrtidia) should be con- 

 sidered here, though they are eroded by currents and 

 waves, and not by run-off. They are fixed and built up by 

 sand- binding grasses and sedges, usually of a hydrophytic 

 nature, and pass ultimately into mesophytic forest. 

 (4) Succession by filling with silt, and 

 plant remains. All aquatic habitats into which silt, 

 wash, or other detritus is borne by streams, currents, floods, 

 waves or tides are slowly shallowed by the action of the 

 water plants present. These not only check the movement 

 of the water, thus greatly decreasing its carrying power, 

 and causing the deposition of a part or all of its load, but 

 they also retain and fix the particles deposited. In accord- 

 ance with the rule, each plant becomes the center of a 

 stabilising area, which rises faster than the rest of the 

 floor, producing the well-known hummocks of lagoons and 

 swamps. All aquatics produce this reaction. It is more 

 pronounced in submerged and amphibious forms than in 

 floating ones, and it takes place more rapidly with greatly 

 branched or dissected plants than with others. In pools 

 {tiphia) and lakes (limnia), debouching streams and surface 

 waters deposit their loads in consequence of the check ex- 

 erted by the still water and the marginal vegetation, and 

 delta-like marshes are quickly built up by filling. Springs 

 (crenia) likewise form marshes where they gush forth in 

 sands, the removal of which is impeded by vegetation. 

 The flood plains and deltas of rivers show a similar reaction. 

 The heavily-laden flood waters are checked by the vege- 

 tation of meadows and marshes, and deposit most of their 

 load. The banks of streams {ochthia) and of ditches 

 (taphria) are often built up in the same fashion by the action 

 of the marginal vegetation upon the current. The pre- 

 sence of marginal vegetation often determines the checking 

 or deflecting of the current in such a way as to initiate 

 meanders, while natural levees owe their origin to it, in 

 part at least. Along low sea coasts, waves and tides hasten 



