44 INTRODUCTION. 



the world, and therefore are little likely to be influenced by 

 any perceptible difference of temperature betwixt the most 

 southerly and the most northerly portions of our British 

 seas. As we do not expect to hear the nightingale in the 

 northern forests of Scotland, or to see the Alpine plants 

 of Ben Xevis blooming in the rich sheltered plains of the 

 south of England, so there are Sea-weeds that are abundant 

 in England that are never found in Scotland, and others 

 that are plentiful in our Scottish seas that are never met 

 with on the genial shores of Devonshire. Dr. Greville, in 

 his admirable ' Algse Britannicae,' observes : — 



" On the shores of the British Islands it is easy to per- 

 ceive that some species, — Gelidium corneum, Vhyllophoi'a 

 ruhens, and Spharococcus coronojji/olins, for example, — be- 

 come plentiful and more luxuriant as we travel from north 

 to south; and, on the other hand, that Ptilota plmtwsa, 

 Hhodomela lycopodioides, and several others, occur more 

 frequently, and in a finer state, as we approach the north. 

 OdordJialia dentata and Hhodijmenia cristata are confined 

 to the northern parts of Great Britaiu, while the Ci/stoseira, 

 Fucus tiiherciilatiLS, Haliseris joolypodioides, Rhodomenia 

 julata, It. Teedii, Microclodia glandulosa, CJiodymenia pin- 

 astroideSy Laurencia tenuiss'wiay Iridcea reniformis, and many 



