INTRODUCTION. XXXV11 



is yet known of the vegetation of extva-europaean seas, that 

 we cannot speak with much minuteness concerning it, but 

 must rest satisfied with a few general and hasty remarks. 

 It appears well established among Algae, as among more 

 perfect plants, that the species of distant seas are, with a 

 few exceptions, different, and this without reference to dif- 

 ference of latitude ; thus it would seem probable that cer- 

 tain species had their centres of growth, from which they 

 are disseminated within a limited range. But Lamouroux 

 observes that they do not radiate from a centre as land 

 plants commonly do, but rather extend in lineal series, fol- 

 lowing the lines of coast, and influenced by a common depth 

 of water : this is, however, merely a modification of the 

 principle that influences the former. There are, however, 

 exceptions to this limitation of species to particular places 

 among Algae, as among phaenogamous plants ; and these 

 are chiefly to be found among the lower tribes, which seem 

 either to have been originally created over the whole sur- 

 face of the earth, or to possess an unlimited power of 

 dispersion. Of this kind are the species of Ulva and En- 

 teromorpha, which are equally abundant in high northern 

 and southern latitudes, as they are under the equator and 

 in temperate regions; nor is there any specific difference 

 observable between plants of these genera from such dif- 

 ferent localities ; they appear to reach an equal degree of 

 perfection in all climates. These have a very low organi- 

 zation, but among those a degree higher up in the scale 

 we find Cod turn tomentosum having a range nearly equally 

 wide ; being found along all the shores washed by the 

 Atlantic and Pacific oceans, from a high northern to a high 

 southern latitude, as well as in the Mediterranean and Bal- 

 tic seas ; having thus a place in the Flora of every country 

 in Europe, of Africa, of both sides of the American conti- 

 nent, and of Australia. Several of the Conferva, which 



