PLANTS AND MOBILE GROUND
51
following intertidal cycle of stability the seedlings by their further growth and curvature attempted to recover the erect position (fig. 11, iii). Again the bank was washed by a spring tide, and such as had failed to advance their roots into the stable grounds below the mobile zone were upset and buried. The final result was that a very small minority of the seedlings (perhaps 1 in 1000) hung on as established plants, notwithstanding the favourable conditions for inoculation and germination. The determining factor for survival was capacity to reach promptly and take root in the stable soil below the mobile zone.
   In the vicissitude just recorded the overwhelming effect of intermittent mobility in the top layer of ground upon seedlings in the act of establishment is clearly shown. But what would have been the consequences if, on another occasion, the seedlings had a few more days in which to lengthen their roots before the spring tide passed over them, so that a very much larger proportion had struck stable ground? The immediate consequence would have been, of course, the survival of a much increased number of plants. But that is not all. In the autumn the Salicornias shed their seed and die. But, as their skeletons remain in situ till the following summer before weathering, they would act as a means of stabilizing the ground, thus largely favouring the conditions for the establishment of the next year’s crop. This favourable influence they exert in two ways. Their roots remain in the soil, thus helping to bind it together, whilst the dead projecting shoots, by causing a local diminution in the rate of flow of the water, appreciably diminish the depth in the soil to which its effect can reach. The result would be a denser colonization of the area, not for that year only but for succeeding years, till the covering reached maximum density.
   It is clear, therefore, that once plants begin to colonize bare ground, the process will rapidly advance till the ground is fully occupied, a result largely due to the cover which the pioneers provide, thereby reducing the mobility of the soil.
   Observations of this kind are to be made everywhere, and it is by their right interpretation and application that progress in foreshore control will be made.
   To recapitulate: we see that mobile ground becomes stabilized