192 PLANT LIFE. 



Shingle Flora. — Occasionally along the shore 

 great accumulations of shingle may be found. These are 

 continually shifting, either with a distinct set in one 

 direction, or backwards and forwards. Very few plants 

 seem able to exist upon the stones unless they have 

 been a very long time at rest and have been covered 

 with a certain amount of soil. Amongst the most 

 characteristic colonisers of shingle are Rosa splnosissiina^ 

 Potentilla anserina, and a few others. Brassica monensis 

 also generally occurs in shingle or gravelly soil mixed 

 with sand. In Scotland special adaptations to this 

 unusual form of the coast have not been traced. 



Sand Flora. — This is also distinctly the case with 

 regard to the next group, or sand-dune plants. On 

 the seaward side of the dunes, which is generally at 

 a very slight slope, will be found the Sea Couch- 

 grass {Agropyruni) and Honckenya peploides. Both 

 have exceedingly long underground stems which are 

 capable of developing under the most unfavourable 

 circumstances, and both are well adapted to the salt, 

 barren, and exposed positions in which they grow. 

 Upon the seaward face of the dune, and upon all the 

 freshly formed hillocks, only the Dune Grass {Ainiiio- 

 phila arundinacea) seems able to develop. The strong 

 stems of this plant are often many feet in length ; its 

 very hard, sharp buds help it to bore a way upwards 

 through several feet of sand. Hence it is difficult for 

 the shifting sand waves to overwhelm it. When the 

 dune has acquired a certain stability through these 

 tough interlacing rhizomes, other plants begin to 

 appear. Generally, these are to be found on the summit 

 of the dune a little way back from the exposed face. 

 Eryngium is one of the first to occur, then Festuca ovina 

 begins to occupy most of the spaces left between the 



