THE SMITHSONIAN INSTITUTION. 119 



BwimSj and only seen by the light of tlie pliosplioric gleam wliicli he 

 emits. Now this exuberant animal creation coultl not be maintained 

 "without a vegetable substructure. It is one of the laws of nature that 

 animals shall feed on organized matter, and vegetables on unorgan- 

 ized. 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 Alg{\3, and we may judge of the completeness with which they 

 execute their mission b}^ the fecundity of the animal world which de- 

 pends upon them. Not that I would assert that all, or nearly all, the 

 marine animals are directly dependent on the Algte 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 Algw, and there are myriads of the lower in organization which do 

 de^iend upon them altogether. 



Among the higher orders of Algas feeders I may mention the Tur- 

 tles, whose green fat, so prized by aldermanic palate, may possibly be 

 colored by the unctuous green juices of the Caulerpce on which they 

 browse. But without further notice of those that directly depend on 

 the Algaj, it is manifest that all must ultimately, though indirectly, 

 depend on whatever agency in the first instance seizes on inorganic 

 matter, and converts it into living substance suitable to enter into the 

 composition of animal nerve and muscle ; and this agency is assur- 

 edly the office of the vegetable kingdom, here confined in the main to 

 Algi\3. We thus sufficiently establish our position that the Algaj are 

 indispensable to the continuance of organic life in the sea. 



As being the first vegetables that prey upon dead matter, and as 

 affording directly or indirectly a pasture to all water animals, the 

 Alga? are entitled to notice. Yet this is but one-half of the task com- 

 mitted to them. Equally important is the influence which their 

 growth exerts on the water and on the air. The well-known fact 

 that plants, whilst they fix carbon in an organized form in extending 

 their bodies by the growth of cells, exhale oxygen gas in a free state, 

 is true of the Alg;i3 as of other vegetables. By this action they tend 

 to keep pure the water in which they vegetate, and yield also a con- 

 siderable portion of oxygen gas to the atmosphere. I have already 

 stated tliat whenever land becomes flooded, or wherever an extensive 

 surface of shallow water — whether fresh or salt — is exposed to the 

 air, Confervce and allied Algre quickly multiply. Every pool, every 

 stagnant ditch is soon filled with their green silken threads. These 

 threads cannot grow without emitting oxygen. If you examine such 

 a pool on a sunny day, you may trace the beads of oxygen on the sub- 

 merged tlireads, or see the gas collect in bubbles where the threads 

 present a dense mass. It is continually passing off into the air while 

 the Conferv^e vegetate, and this vegetation usually continues vigor- 

 ous, one species succeeding another as it dies out, as long as the pool 

 remains. And when, on the drying up of the land, the Confervas die, 

 their bodies^ which are scarcely more than membranous skins filled 

 with fluid, shrivel up, and are either carried away by the wind or 

 form a papery film over the exposed surface of the ground. In neither 



