2 OCEAN LIFE. 



lower part of the stem. The only instances of penetrating roots 

 among the Algae, with which I am acquainted, occur in certain 

 genera of Sophoneae and in the Caulerpeae, tropical and sub-tro- 

 pical forms. But neither in these cases do the roots appear to 

 differ from the nature of holdfasts, and their ramification and 

 extension through the sand is probably owing to the unstable 

 nature of such a soil. It is not in search of nourishment, but of 

 stability, that the fibres of their roots are put forth, like so many 

 tendrils." 



Three principal varieties of color are generally noticed among 

 the Algae, namely : grass-green or herbaceous, olive-green, and 

 red. In the sub-division of Algae into three groups, the color 

 of the frond is employed as a convenient diagnostic character. 

 The sea, in all explored latitudes, has a vegetation of Algae. To- 

 warda the poles this is restricted to microscopic kinds, but almost 

 as soon as the coast rock ceases to be coated with ice, it begins 

 to be clothed with Fuci. Climate has an effect on the Algae as 

 upon all other organic bodies, though its influence is less percep- 

 tible in them than in the terrestrial plants, because the tempera- 

 ture of the sea is much less variable than that of the air. Still, 

 as the temperature of the ocean varies with the latitude, we find 

 in the marine vegetation a corresponding change ; certain groups 

 being confined to the colder regions of the sea, and others only 

 vegetating where the mean temperature is considerable. The 

 uses of the Algae may be considered under two points of view, 

 namely : the general office which this great class of plants, as a 

 class, discharges in the economy of nature ; and those minor use- 

 ful applications of separate species which man selects on dis- 

 covering that they can yield materials to supply his various 

 wants. The part committed to the Algae in the household of 

 nature, though humble when we regard them as the lowest organic 

 members in that great family, is not only highly important to 

 the general welfare of the organic world, but, indeed, indispens- 

 able. This we shall at once admit, when we reflect on the vast 

 preponderance of the ocean over the land on the surface of the 

 earth, and bear in mind that almost the whole submarine vegeta- 

 tion consists of Algae. 



It is one of the laws of nature, that animals shall feed on 



