INTRODUCTION. XXXIX 



of vegetation peculiar to itself, which extends to the ex- 

 tremity of the Black Sea ; and notwithstanding their geo- 

 graphical proximity, the plants of the port of Alexandria 

 or of the coast of Syria differ almost entirely from those of 

 Suez and the Red Sea." To these regions we may add 

 the Chinese and Japanese seas, which contain many re- 

 markable and peculiar forms. Too little is known of the 

 east coast of Africa, or of the southern ocean, to speak po- 

 sitively of them; and of the vegetation of the Caspian we 

 are completely ignorant. The shores of South Africa, while 

 they possess many species peculiar to themselves, exhibit 

 a vegetation in many respects analogous to that of Australia, 

 with, however, some remarkable deficiencies: thus, among 

 the most curious types of structure, Splachnidium rugosum 

 is common to both ; a species of Champia has lately been 

 brought from Van Dieman's Land ; and at Port Natal there 

 is a plant analogous to Claudea ; and, if we may trust Von 

 Suhr, Gelidium lucidum and Rhodymenia Lamberti occur 

 at Algoa Bay : but with these similarities to the vegetation 

 of Australia, there is a remarkable deficiency at the Cape 

 of the genus Blossevillea, a peculiar and extensive group, 

 which gives, as we shall presently see, a prominent feature 

 to the marine vegetation of Australia. 



Many powerful causes, independently of climate, un- 

 doubtedly tend to limit the distribution of Algae. The in- 

 tervention of great depths of the ocean between localities 

 favorable to their growth, has, as Lamouroux aptly remarks, 

 a similar and analogous influence on sea plants, as the ex- 

 istence of high mountain ranges exercises on those of the 

 land ; the presence of extensive sand banks, which are as 

 much sub-marine deserts as the sandy tracts of continents, 

 are unfavorable to vegetation ; strong currents ; projecting 

 capes ; the fresh waters of great rivers ; and a change of 

 soil ; all these interpose to prevent the wide dissemination 



