42 THE BIOLOGY OF THE SEA-SHORE 



sandy mud formations, (c) salt marsh formations, and in 

 addition (d) vegetation of river mouths, (e) vegetation of 

 brackish bays. 



Johnson and York (191 5), as a resuh of their investiga- 

 tions carried out at Cold Spring Harbour (U.S.A.) between 

 1905 and 1913, recognised five vegetational zones or belts. 

 I, Plankton ; H, Bottom Vegetation ; HI, Mid-littoral belt 

 (i*5 to 6*5 feet), characterised by Spartina glahrdy Fucus, 

 Ascophyllum, etc. ; IV, Upper Littoral belt (8-12 feet) 

 vegetation varied, Salicorniay Spartina patens, Suceda, 

 Scirpus ; V, Supra Littoral belt (8-12 feet) less clearly 

 defined ; chief plants Ammophila, Solidago, Salsola, Cakile, 

 Scirpus, Lathyrus, Aster, and others. The authors believe 

 that " the vertical range of a littoral plant is exactly pro- 

 portional to the range of the tide and give " Habit Analysis 

 Tables " for each plant, with the following particulars : 

 salinity of soil water ; light demands ; upper limit ; lower 

 limit ; average emergence per lunar day ; average sub- 

 mergence per lunar day ; ratio of submergence to emer- 

 gence : {a) at lower limit, {b) at higher Umit. 



Currents disseminate seeds and spores, and break off 

 and transport shoots of Zostera, Ulva, Fucus, etc. ; or on 

 the other hand retard extension by causing mechanical 

 injury. Rapid movement favours some forms by increasing 

 the interchange of material between plant and water, and 

 possibly also by excluding competitors (Johnson and York, 

 op. cit.). 



On the open shore organic matter cannot accumulate 

 much, nor in strong currents and tidal scour. Only in the 

 sheltered parts of estuaries, creeks, lagoons, etc., can such 

 deposits take place in quantities. On the open coast decay- 

 ing organic matter (animal and vegetable) may be found under 

 fixed stones, boulders, etc., and there offers a suitable habitat 

 to certain types of animal life. Atmospheric moisture plays 

 an important part in connection with the littoral vegetation, 

 and the problem of desiccation during low tide is complex ; 

 latitude and the accompan)dng climatic conditions (wind, 

 sunshine, etc.), together with situation and aspect, cause 



