OR, THE HOME-CULTURE OF FRESH-WATER PLANTS. 
length of time, though the experiment he was pro¬ 
secuting was for another and perfectly distinct 
purpose—that of ascertaining the true vegetable 
nature of corallines. Dr. Dankester, in his capital 
treatise on the Aquarium, states that he kept Stickle¬ 
backs in a glass vessel with a plant of Yalisneria, in 
1849, which was, in fact, a true Aquavivarium upon 
principles now adopted ; but he did not then an¬ 
nounce it as a discovery, nor probably consider it as 
such. Mr. E». Warrington was, in fact, the first 
(in 1850) to publish , in a paper communicated to 
the Chemical Society, a series of observations upon 
the subject. In that essay he entered, with some 
detail, into the functions assigned to plants for the 
conversion of carbonic acid gas into oxygen, and the 
consequent necessity of their presence for the pre¬ 
servation of animal life, which would otherwise, by 
the quantity of carbonic acid which it throws off, 
become poisoned by its own secretions. He further 
stated clearly that a third, or cleansing agency, 
was absolutely necessary, inasmuch as certain por¬ 
tions of plants, or the whole, having arrived at ex¬ 
treme maturity, naturally perished, and that the de¬ 
caying matter so produced was calculated to cause 
as much injury as the superabundance of carbonic 
acid, or the absence of oxygen. In fact, parts of 
11 
