IV. 
INTRODUCTION. 
21 
effect to height in the other ; and the Algie 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 serial 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 Algae of higher 
organization than the Diatomacece. 
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 recorded 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 Algae 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. FI. 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 Algie of the north temperate zone. 
Humboldt, in his “ Personal Narrative” mentions having dredged a plant to 
which he gave the name Fucus vitifolius , (probably a Codlum 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 Algae growing near the 
surface. I possess a specimen of Anadyomene stellata dredged at the depth of 20 
fathoms, in the Gulpli 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 Aegean 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 Algie vegetate. I 
say, ordinary Algae, for it will be remembered that Diatomaceie exist in the pro- 
found abysses of the ocean, as far as we are acquainted with them. 
And besides these microscopic vegetables, Algae of a group called Nidlvpores or 
Corallines (Corollinacew), 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 Nullipores are 
scarcely distinguishable, by the naked eye, from any ordinary calcareous incrus- 
