MAEINE BOTANY. 7 



tion equally exists beneath the waters as on land. Fewer 

 divisions undoubtedly there are, because sea plants, unlike 

 those of terrestrial rock or soil, are not liable to be affected 

 by atmospheric changes ; the sun does not scorch them 

 during summer, nor may the frosts of winter depress their 

 vital energy; and hence it happens that sea- weeds are 

 more uniformly dispersed. 



The vast extent of ocean greatly facilitates such a general 

 dispersion. Land plants are continually impeded in their 

 progress by intervening seas, or rivers ; marine plants 

 rarely by land barriers, although the number of tribes into 

 which marine botanists have divided the family of Algae are 

 very numerous, and their watery stations singularly varied. 

 Those stations, as far as the researches of indefatigable 

 naturalists extend, have each an especial reference to the 

 character and mode of growth pertaining to aquatic plants, 

 or to the necessities of such marine animals or shell-fish as 

 harbour among them. Numerous species remain stationary, 

 growing on the stony bed of ocean, or clinging to the rocks 

 — others become attached to the shells of crustaceous or 

 testaceous wanderers, and travel with them — others, again, 

 float hither and thither, having no abiding-place. 



" Hung from the rock, on ocean's foam to sail, 

 "Where'er the surge may sweep, the tempest's breath prevail." 



Such plants range through various geographical regions 

 of aquatic floras, being found deposited on the shores of 

 countries separated by the "liquid weight of half the 

 globe," as, for example, those of Europe and the United 

 States ; of Cape Horn and of Van Diemen's Land. Among 

 species strictly antarctic, Dr. Hooker identified not less than 

 a fifth-part of the whole species common to the British seas. 

 This eminent naturalist suggested, that cold currents, which 

 prevail from Cape Horn to the Equator, and are there met 

 by other streams of similar temperature, may, by their 

 direct influence, as well as temperature, facilitate the pro- 



