AND THE STRUCTURE OF PLANTS. 91 



that their petals are not special organs, but stamens in an abortive or trans 

 formed state.* 



Plants are also possessed of cutaneous secernents or perspiratory vessels ; 

 and in many plants the quantity of fluid thrown off by this emunctory is very 

 considerable. Keil, by a very accurate set of experiments, ascertained that 

 in his own person he perspired 31 ounces in twenty-four hours. Hales, by 

 experiments equally accurate, determined that a sun-flower, of the weight of 

 three pounds only, throws off 22 ounces in the same period of time, or nearly 

 half its own weight. To support this enormous expenditure it is necessary 

 that plants should be supplied with a much larger proportion of nutriment than 

 animals ; and such is actually the fact. Keil ate and drank 41b. lOoz. in the 

 twenty-four hours. Seventeen times more nourishment was taken in from 

 the roots of the sun-flower than was taken in by the man. 



Plants, nevertheless, do not appear to have the smallest basis for sensation, 

 admitting that sensation is the result of a nervous system ; and we are not 

 acquainted with any other source from which it can proceed : notwithstand- 

 ing that Percival and Darwin, as already observed, have not only endowed 

 them with sensation, but with consciousness also ; and the latter, indeed, with 

 a brain, and the various passions and some of the senses to which this organ 

 gives birth.f 



Yet, though the vessels of plants do not appear to possess any muscular 

 fibres, we have evident proofs of the existence of a contractile and irritable 

 power from some other principle ; and a variety of facts concur in making it 

 highly probable that it is by the exercise of such a principle that the differ- 

 ent fluids are propelled through their respective vessels : nor is there any 

 other method by which such propulsion can be reasonably accounted for. 

 Grew ascribed the ascent of the sap to its levity, as though acting with the 

 force of a vapour : Malpighi, to an alternate contraction and dilatation of the 

 air contained in what he erroneously conceived to be air-vessels : Perrault to 

 fermentation : Hales and Tournefort, to capillary attraction : not one of which 

 theories, however, will better explain the fact than another, as Dr. Thomson 

 has ably established; as he has also the probability of a contractile power in 

 the different sets of vessels distributed so wonderfully over the vegetable 

 frame.J 



That a contractile power may exist independently of muscular fibres, we 

 have abundant proofs even in the animal system itself. We see it in the 

 human cutis or skin, which, though totally destitute of such fibres, is almost 

 for ever contracting or relaxing upon the application of a variety of other 

 powers ; powers external and internal, and totally different in their mode of 

 operation. Thus, austere preparations and severe degrees of cold contract 

 it very sensibly : heat, on the contrary, and oleaginous preparations, as sen- 

 sibly relax it. The passions of the mind exercise a still more powerful effect 

 over it : for while it becomes corrugated by fear and horror, it is smoothed and 

 lubricated by pleasure, and violently agitated and convulsed by rage or anger. 



Yet, could it even be proved that the vessels of plants are incapable of 

 being made to contract by any power whatever, still should we have no great 

 difficulty in conceiving a circulatory system in animals or vegetables without 

 any such cause, while we reflect that one-half of the circulation of the blood 

 in man himself is accomplished without such a contrivance ; and this too, 

 the more difficult half, since the veins, through the greater extent of their 

 course, have to oppose the attraction of gravitation instead of being able to 

 take advantage of it. It is in the present day, however, a well-known fact, 

 and has been sufficiently ascertained by the late Dr. Parry of Bath, and on 

 the Continent by Professor Dollinger, that the contractile power of the mus- 

 cular fibres is not called into action even by the arteries in the course of the 

 ordinary circulation of the blood, since, as we shall have occasion to observe, 

 no increase of size or change of bulk of any kind takes place in arteries 

 either in the contraction or dilatation of the heart's ventricles in a state of 



* M6m. de la SocitHe d'Arcueil, torn. iii. t Willdenow, Princip. of Botany, 226 



J Syst. of Chem. vol. v. p. 388. 1807 



