186	PLANT WINNING OF TIDAL LANDS
marsh as consist predominantly of Armeria (as on the Dovey estuary in Wales and elsewhere), or of Statice (as is so frequently the case in East Anglia), are examples of a survival of the fittest under the given conditions. At the same time, however, it has to be borne in mind that a like result (i.e. a relatively pure sward of a given species of plant) may in some cases arise in the absence of competition, when other plants for any reason are unable to establish, or when their seeds fail to invade the particular area.
   Spergularia media differs somewhat in habit from the other species enumerated in that the cylindrical fleshy leaves are borne in whorls on spreading, straggling axes which arise from the summit of the subterranean rhizome. As these axes become bedded in, they in turn originate fresh branches in the same manner.
  The Reproductive Methods of Salt-marsh Plants.—The annual plants, of which the Salicornias (S. annua, S. ramosis-sima) and Suceda maritima are the best examples, depend for their power of holding their place upon their huge seed output. When these plants die in autumn the seeds fall in the mud and become anchored by the filamentous Algie (Rhizoclonium, &c.). Under cover of these they germinate in early spring, coming up in beds, thick like mustard and cress. Germination under this protection is considerably earlier and under more favourable conditions than on bare mud. Thermometers placed beneath the algal network on a cold day in March showed a mean excess of 2° C. over the temperatures given by simultaneous readings from other thermometers similarly placed, except that the algae had been cleared away.
   By no means the whole of the seeds are thus entrapped; many drift and are carried to a variety of situations. Thus if slabs of the soft, bare mud of creek bottoms be removed and placed under appropriate conditions, seedlings will often appear (Suaeda, Salicornia), which under ordinary circumstances hardly ever establish on account of the high mobility of the mud.
   These annuals are able to hold their own year after year even when embedded in a turfy matrix of the Salt-marsh Grass (Glyceria maritima). This they appear to do in virtue of their