INTRODUCTIOJf. 31 



USES OF THE ALGiE. 



The uses of the Alga3 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 useful applications of separate species which man 

 selects on discovering that they can yield materials to supply his various wants. 



The part committed to the Algaj 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, 

 indispensable. This we shall at once admit, when we reflect on the vast prepon- 

 derance of the ocean over the land on the surface of the earth, and bear in mind 

 that almost the whole submarine vegetation consists of Algce. The number of 

 species of marine plants which are not Algee proper is extremely small. These on 

 the American coast are limited to less than half a dozen, only one of which, the 

 common Eel Grass (Zostera marina), is extensively dispersed. 



All other marine plants are referable to Alga3 ; the wide spread sea would there- 

 fore be nearly destitute of vegetable life were it not for their existence. Almost 

 every shore — where shifting sands do not forbid their growth — is now clothed with 

 a varied band of Algte of the larger kinds ; and microscopic species of these vege- 

 tables (Diatomacece) teem in countless myriads at depths of the ocean as great as 

 the j)lummet has yet sounded, and where no other vegetable life exists. It is not 

 therefore, speaking too broadly to say that the sea, in every climate and at all 

 known depths, is tenanted by these vegetables under one phase or other. 



The sea, too, teems with animal life, — that " great and wide sea, wherein are 

 things creeping innumerable, both small and great beasts," aifords scope to hordes 

 of animals, from the "Leviathan" whale to the microscopic polype, transparent as 

 the water in which he swims, and only seen by the light of the phosphoric gleam 

 which he emits. Now this exuberant animal creation could not be maintained 

 Avithout a vegetable substructure. It is one of the laws of nature that animals 

 shall feed on organized matter, and vegetables on unorganised. For the support 

 of animal life, therefore, we require vegetables to change the mineral constituents 

 of the surrounding media into suitable nutriment. 



In the sea this office of vegetation is almost exclusively committed to the Algaj, 

 and we may judge of the completeness with which they execute their mission by 

 the fecundity of the animal world which depends upon them. Not that I would 

 assert that all, or nearly all, the marine animals are directly dependant on the Algaj 

 for their food ; for the reverse is notoriously the case. But in every class we find 

 species which derive the whole or a part of their nourishment from the Alga?, 

 and there are myriads of the lower in organization which do depend upon them 

 altogether. 



Among the higher orders of Algaj feeders I may mention the Turtles, whose green 

 fat, so prized by aldermanic palate, may possibly be coloured by the unctuous green 

 juices of the CaulerpcB on which they browse. But without further notice of those 

 that directl)^ depend on the Alga?, it is manifest that all must ultimately, though 



