iv THE LESSON OF THE BRITISH FLORA 39 



xerophilous habit, and we may extend this view to other temperate 

 strand-floras. 



(4) But this xerophilous habit is also characteristic of inland 

 plants in certain localities, as of those of the steppe, the desert, the 

 rocky mountain-top, and of other exposed situations, in all of 

 which checks to the loss of water by transpiration are required. 

 Whilst the risks of drought are thus guarded against in the case of 

 plants stationed in arid localities, the risk of injury to the plant 

 from the accumulation of salt in the tissues is obviated in the 

 instance of the plants of the coast. 



(5) On the other side we have the hygrophilous habit 

 characteristic of plants living under conditions where checks to 

 transpiration are relatively little needed. All the plants of the 

 margins of rivers and ponds belong here, and indeed all plants 

 living under moist conditions. 



(6) This distinction between the xerophilous and hygrophilous 

 habits penetrates deeply into all questions connected with stations, 

 and lies behind all matters relating to the buoyancy of seeds or 

 fruits. It is the fitness or unfitness of a plant for living in dry 

 situations that primarily determines the station. If a xerophilous 

 plant has a buoyant seed or seedvessel it finds its way ultimately 

 to the coast ; if it is hygrophilous and its seeds or fruits can float, 

 then it is finally established on the side of a pond or river. 



(7) The composite character of the British strand-flora is to be 

 explained on the above principles. We have in the first place the 

 plants confined to the sandy beach, many of which possessing 

 buoyant seeds or fruits are dispersed by the currents. Next come 

 the plants of the sandy beach which are found also far inland in 

 open plains and on mountain-tops ; and afterwards come the plants 

 of the salt-marsh and mud-flats of the coast, which appear again 

 in the saline plains and swamps in the interior of the continents. 



(8) The plant-formation of the river's border displays also 

 lines of division, and is by no means homogeneous ; and indeed 

 other factors besides those connected with seed-buoyancy have 

 here been in operation. 



(9) In only a few of the possible stations of British plants can 

 a direct connection be traced with seed-buoyancy. Yet it is at 

 these few stations, such as at the coast and by the pond or river, 

 that the plants with buoyant seeds and fruits have mainly gathered. 



(10) The plants now frequenting wet stations may often be 

 regarded as the remains of an age when moist conditions for 

 plant-life prevailed. 



