122 



HISTORY OP THE VEaETABLE KINGDOM. 



appeared above ground nine days sooner than 

 the former, and produced twenty-five beans ; 

 while the fonner produced only fifteen. Now the 

 result of this experiment, as well as the preced- 

 ing facts, is evidently favourable to the pre- 

 sumption of Senebier, and shows that, if carbonic 

 acid is not the state in which carbon enters the 

 plant, it is at least a state preparatory to it ; and 

 there are other circumstances tending to corro- 

 borate the opinion resulting from the analysis of 

 the ascending sap of plants. The tears of the 

 vine, when analysed by Senebier, yielded a por- 

 tion of carbonic acid and earth ; and as the as- 

 cending sap could not be supposed to have yet 

 undergone much alteration, the carbonic acid, 

 like the earth, was probably taken up from the 

 soil. 



But this opinion, which seems to be so finnly 

 established upon the basis of experiment, Ilas- 

 senfratz strenuously controverts. According to 

 experiments which he had instituted witli an 

 express view to the investigation of this subject, 

 plants which were raised in water impregnated 

 with carbonic acid, differed in no respect from 

 such as grew in pure water, and contained no 

 carbon that did not previously exist in the seed. 

 Now if this were the fact, it would be decisive 

 of the point in question. But it is plain from 

 the experiments of Saussure, as related in a pre- 

 ceding section, that Hassenfratz must have been 

 mistaken, both with regard to the utility of 

 carbonic acid gas as furnisliing a vegetable ali- 

 ment, and with regard to the augmentation of 

 carbon in the plant. The opinion of Senebier, 

 therefore, may still be correct. 



It must be acknowledged, liowever, that the 

 subject is not yet altogether satisfactorily cleared 

 up; and that carbon may certainly enter the 

 plant in some state different from that either of 

 charcoal in solution, or of carbonic acid gas. Is 

 not the carbonic acid of the soil decomposed 

 before entering the plant? Tbis is a conjecture of 

 Dr Thomson's, founded upon tlie following facts: 

 The green oxide of iron is capable of decom- 

 posing carbonic acid; and many soils contain 

 that oxide. Most soils indeed, contain iron, 

 either in the state of the bro-\vn or green oxide, 

 and it has been found that oils convert the bro\vn 

 oxide into green. But dung and rich soils con- 

 tain a quantity of oily substance. One effect of 

 manures, therefore, may be that of reducing the 

 brown oxide of iron to the green, thus rendering 

 it capable of decomposing carbonic acid gas, so 

 ns to prepare it for some new combination, in 

 which it may serve as an aliment for plants. 

 All this, however, is but a conjecture; and it is 

 more probable that the carbonic acid of the soil 

 enters the root in combination with some other 

 substance, and is afterwards decomposed witliin 

 the plant itself. 



CHAP. XIX. 



OF VEOETADLE VITALITr. 



Vegetables, as we have already remarked, 

 differ entirely from mineral bodies, in possessing 

 an organized structure; and in obeying laws 

 totally different from those which regulate in- 

 organic matter. In tliis respect, they nearly re- 

 semble animal bodies; and hence, both are said 

 to be endowed with life or vitality. So little is 

 known, however, of the nature of this vitality, 

 either in animals or vegetables, that it need not 

 be surprising if a variety of conflicting theories 

 have been formed by physiologists, to account 

 for its primary cause. While some affirm that 

 the vital actions are the result simply of an or- 

 ganized structure, acted upon by external stimuli; 

 others are disposed to believe in a distinct prin- 

 ciple of vitality, which, acting by peculiar laws, 

 moulds and regulates inorganic matter, so as to 

 exhibit all the phenomena of life. 



One of the chief arguments in support of a 

 principle of vitality, is the fact that organized 

 bodies are thereby rendered capable of resisting, 

 and counteracting the ordinary laws of chemical 

 affinity. This circumstance, which seems to 

 have been first established by Humboldt, is obvi- 

 ously applicable to the case of animals; as is 

 proved by their processes of digestion and as- 

 simulation, whereby the food is converted into 

 chyle and blood, as well as from tlie various se- 

 cretions of their several organs, effecting tho 

 growth and development of the individual, in 

 direct opposition to the laws of chemical affinity, 

 which, as soon as this principle of vitality ceases 

 to operate, immediately begin to give indications 

 of their action in the incipient symptoms of the 

 putrefaction of tho dead body, and its ultimate 

 resolution into the elements of which it was 

 formed. Tliis rule is also applicable to vegeta- 

 bles, as is illustrated in a similar manner by tlie 

 ascent of the sap, and its ultimate elaboration 

 into the various substances proper to the plant, 

 by a series of operations contrary both to the 

 laws of gravity and chemical action. At the 

 death of the plant, too, and on the cessation of 

 its principle of vitality, the usual chemical 

 agencies are resumed, and a similar decomposi- 

 tion takes place, as in the case of animals. 

 The vegetable economy, therefore, exliibits phe- 

 nomena totally different from that which char- 

 acterises minoi'al and inorganic bodies. Vegeta- 

 ble life, therefore, is uphold by different and 

 peculiar laws; and it may be, is in its essence a 

 peculiar principle, distinct from the matters 

 which it moulds and forms into various shapes 

 and textures. Vegetable life, then, is charac- 

 terised by the following properties. 



Excitability, A remarkable property of or- 



