COMPOSITION OF PLANTS. 22'i 



II. On the Common Sap. 



347. 



The matters which plants attract from the soil, are not 

 for tlie most part its compound ingredients ; tliey do not 

 attract either earth, or metals, or salts, or extractive mat- 

 ter ; but, according to all observations and experiments, 

 they take up only carbonic acid water, united with azote ; 

 and all improvements of the soil, all manuring of it, have 

 no other object than that of increasing this sap, for the 

 purpose of evolving more powerfully, and in due proportion, 

 its proper products. From the time of Helmont, it has been 

 understood, that water is the only source of all the nourish- 

 ment of vegetables. Plants have long been reared amidst 

 circumstances of such a nature, that no earthly ingredients at 

 least could be taken up by them. The experiments of Bon- 

 net, Kraft, and Duhamel, are the most decisive on this 

 point. In later times, it has been completely established by 

 Ingenhousz, Percival, Schrader, and Braconnot, that plants 

 thrive amidst substances that are altogether insoluble, pro- 

 vided they are supplied with carbonic acid water, and that 

 they even present the same constituent parts, as when they 

 are reared in the earthy soil. 



And this account is strengthened by the necessity which is 

 known to exist, for exposing any soil, the chief ingredient of 

 which is carbon, to the influence of the air, that oxygen may 

 be attracted, and carbonic acid be thereby formed. The 

 careful and complete turning up of Clover and Lucern fields 

 in spring, not only loosens the soil, but promotes also the pro- 

 duction of carbonic acid. Hence the repeated ploughings, 

 by means of which Peter Kretschmar, seventy years ago, 

 wished to render manure needless, must have turned out very 

 unprofitable. 



If we reflect still farther on the recent experiments which 

 have shewn, that there is a considerable consumption of 

 carbonic acid from absorption by the leaves ; and if we con- 

 sider that all those circumstances are favourable to the growth 



