THE SHORES OF BRITAIN. 51 



obvious claim to our consideration, except that, in 

 common with other sea-plants, it gives out oxygen, 

 and thus maintains the element in which it grows in 

 a state fit for the support of animal life. But this is 

 a service vastly important, and explains why the 

 " floor of the ocean " is covered, as it appears to 

 be, with such a profusion of vegetable life. And 

 here so wisely is the balance kept up between the 

 animals which absorb oxygen and the plants which 

 evolve it, that, perhaps, the world could not lose a 

 single species of either without derangement of the 

 existing order, which would be followed by manifest 

 inconvenience. Of course our Little Coralline cannot 

 do much to promote this object ; but that it does 

 exert some beneficial influence, we have evidence in 

 an experiment of Dr. Johnston's, whose researches on 

 these neglected tribes are so interesting. " Was there 

 a need," he observes, " of adding any additional proof 

 of the vegetability of the Corallines, an experiment 

 in progress before me would seem to supply it. It is 

 now eight weeks ago since I placed in a small glass 

 jar, containing about six ounces of pure sea-water, a 

 tuft of the living Corallina officinalis, to which were 

 attached two or three minute Confervce, and the very 

 }-oung frond of a green Ulva, while numerous Rissoce, 

 several little Mussels and Annelides, and a Star-fish, 

 were crawling amid the branches. The jar was 

 placed on a table, and was seldom disturbed, though 

 occasionally looked at ; and at the end of four weeks 

 the water was found to be still pure, the Mollusca 

 and other animals all alive and active, the Confervce 

 had grown perceptibly, and the Coralline itself had 



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