62 PLANTS PARTLY SUPPORTED BY THE AIR Ax\D BY THE SOIL. 



cither extremity — on the warmth and moisture of the climate — on the du- 

 ration and intensity of the sunshine, and other circumstances of a similar 

 kind — so that the only general law seems to be, that, like animals, plants 

 have also the power of adapting themselves, to a certain extent, to the 

 conditions in which they are placed ; and of supporting life by the aid of 

 such sustenance as may be within their reach. 



Such a view of the course of nature in the vegetable kingdom, is con- 

 sistent, I believe, with all known facts. And that the Deity has bounti- 

 fully fitted the various orders of plants — with which the surface of the 

 earth is at once beautified and rendered capable of supporting animal 

 life — to draw their nourishment, in some spots more from the air, in oth- 

 ers more from the soil, is only in accordance witli the numerous provisions 

 we everywhere perceive, for the preservation and continuance of the 

 present condition of things. 



By taking a one-sided view of nature, we may arrive at startling 

 conclusions — correct, if taken as partial truths, yet false, if advanced as 

 general propositions — and fitted to lead into error, such as have not the 

 requisite knowledge to enable them to judge for themselves — or such as, 

 doubtful of their own judgment, are willing to yield assent to the author- 

 ity of a name. 



Of this kind appears, at first sight, to be the statement of Liebig, that 

 "when a plant is quite matured, and when the organs by which it ob- 

 tains food from the atmosphere are formed, the carbonic acid of the soil 

 is no further required" — and that, "during the heat of summer it derives 

 its carbon exclusively from the atmosphere." — [Organic Chemistry ap- 

 plied to Agriculture, p. 48.] 



A little consideration will shew us that, while the proposition contained 

 in the former quotation may be entertained and advanced as a matter of 

 opinion — the latter is obviously incorrect. In summer, when the sun 

 shines the brightest, and for the greatest number of hours, the evapora- 

 tion from the leaves of all plants (their insensible perspiration) is the 

 greatest — the largest supply of water, therefore, must at this season be 

 absorbed by the roots, and transmitted upwards to the leaves. — [Lindley's 

 Theory of Horticulture, p. 46.] — Butthis water, before it enters the roots, 

 has derived carbonic acid and other soluble substances from the air and 

 from the soil, in as large quantity at this period as at any other during 

 the growth of the plant ; and these substances it will carry with it in its 

 progress through the roots and the stem. 



Are the functions of tlie root changed at this stage of the plants' 

 growth ? Do they now absorb pure water only, carefully separating and 

 refusing to admit even such substances as are he\d m solution? Or 

 do the same materials which minister to the growth of the plant in its 

 earlier stages, now pass upwards to the leaf and return again in the 

 course of the circulation unchanged and unemployed, to be again re- 

 jected at the roots ? Does all this take place in the height of summer, 

 while tlie plant is still rapidly increasing in size ? The opinion is nei- 

 ther supported by facts nor consistent with analogy. 



But such an opinion, — however the words above quoted may mislead 

 some, — is not intended to be advanced by Liebig; for, in the following 

 j)age he says, that "the power which roots possess of taking up nourish- 

 ment does not cease so long as nutriment is present." In summer, 



