IV. 



INTRODUCTION. 21 



effect to height in the other ; and the Alga? of deep parts of the sea are to those of 

 tidal rocks, as alpine plants are to littoral ones. In both cases there is a limit to 

 the growth of species ; each terial species having a line above which it does not 

 vegetate, and each marine one, a line beyond which it does not descend. And as, 

 at last, we find none but the least perfect lichens clothing the rocks of high 

 mountains, so in the sea beyond a moderate depth are found no Algce of higher 

 organization than the Diatomacew. 



These latter atomic plants would appear to exist in countless numbers at very 

 extraordinary depths, having been constantly brought up by the lead in the deep 

 sea soundings recoi'ded in Sir James Ross's Antarctic voyage. But ordinary sea 

 plants cease to vegetate in comparatively shallow water, long before animal life 

 ceases. The limits have not been accurately ascertained, and are probably much 

 exaggerated as commonly given in books. 



Lamouroux speaks of ordinary Algse growing at 100 to 200 fathoms, but we 

 have no exact evidence of the existence of these plants at this great depth. The 

 Macrocystis, the largest Alga known, has sometimes been seen vegetating in 40 

 fathoms (Hook. Fl. Ant. vol. 2, p. 464j water, while its stems not merely reached 

 the surface, but rose at an angle of 45° from the bottom, and streamed along the 

 waves for a distance certainly equal to several times the length of the " Erebus ;" 

 data which, if correct, give the total length of stem at about 700 feet. Dr. 

 Hooker, however, considers this an exceptional case, and gives from eight to ten 

 fathoms as the utmost depth at which submerged seaweed vegetates in the southern 

 temperate and Antarctic ocean ; a depth which is probably much exceeded in the 

 tropics, and which is at least equalled by Alga; of the north temperate zone. 



Humboldt, in his "Personal Narrative" mentions having dredged a plant to 

 which he gave the name Fucus vitifoHus, (probably a Coclium or Flabellaria) in 

 water 32 fathoms deep, and remarks that, notwithstanding the weakening of the 

 light at that depth, the colour was of as vivid a green as in Alga? growing near the 

 surface. I possess a specimen of Anadyomene stellata dredged at the depth of 20 

 fathoms, in the Gulph of Mexico, by my venerable friend the late Mr. Archibald Men- 

 zies, and it is as green as specimens of the same plant collected by me between tide 

 marks at Key West, and is much more luxuriant. 



Professor Edward Forbes, whose admirable report on the ^gean Sea should be 

 consulted by all persons interested in the distribution of life at various depths, 

 dredged Constantinea reniformis. Post, and Rupr. in 50 fathoms, the greatest depth 

 perhaps on record, as accurately observed, at which ordinary Alga3 vegetate. I 

 say, ordinary Alga3, for it Avill be remembered that Diatomacea3 exist in the pro- 

 found abysses of the ocean, as far as we are acquainted Avith them. 



And besides these microscopic vegetables, Algse of a group called NuUipores or 

 Corallines (Corollinacem), long confounded with the Zoophytes, become more numer- 

 ous as other Algae diminish, until they characterize a zone of depth where they 

 form the whole obvious vegetation. These remarkable plants assimilate the mu- 

 riate of lime of seawater and form a carbonate in their tissues, which from the 

 great abundance of this deposit become stony. The less perfect NuUipores are 

 scarcely distinguishable, by the naked eye, from any ordinary calcareous incrus- 



