90 



ON ORGANIZED BODIES, 



mon balsamine,*or of various other plants, and cut it horizontally at its lower 

 end, and plunge it, so cut, into a decoction of Brazil wood, or any other 

 coloured fluid, we shall perceive that the arteries or adducent vessels, as also 

 the lacteals, will become filled or injected by an absorption of the coloured 

 liquor; but that the veins, or reducent vessels, will not become filled; of 

 course evincing an obstacle, in this direction, to the ascent of the coloured 

 fluid. But if we invert the stem, and in like manner cut horizontally the ex- 

 tremity which till now was uppermost, and plunge it so cut into the same 

 fluid, we shall then perceive that tlie veins will become injected, or suff"er the 

 fluid to ascend, but that the arteries will not : proving clearly the same kind 

 of obstacle in the course of the arteries in this direction, which was 

 proved to exist in the veins in the opposite direction ; and which reverse 

 obstacles we can scarcely ascribe to any other cause than the existence of 

 valves. f 



By this double set of vessels, moreover, possessed of an opposite power, 

 and acting in an opposite direction, the one to convey the sap or vegetable 

 blood forwards, and the other to bring it backwards, we are able very suffi- 

 ciently to establish the phenomenon of a circulatory system ; and, according 

 to several of the experiments of M. Willdenow, it seems probable that this 

 circulatory system is maintained by the projectile force of a regular and alter- 

 nate contraction and dilatation of the vegetable vessels. Yet the great minute- 

 ness of these vessels must ever render it extremely difficult to obtain any 

 thing like absolute certainty upon this subject. Even in the most perfectly 

 established circulatory systems of animals, in man himself, it is not once in 

 five hundred instances that we are able to acquire any manifest proof of such 

 a fact : we are positive of the existence of an alternating systole and diastole 

 in the heart, from the pulsation given to the larger arteries when pressed 

 upon ; but no degree of pressure produces any such pulsation in the minuter 

 arteries, at least, in a healthy state; yet we have full reason to believe that 

 the same action of the heart extends to the minutest as to the largest arte- 

 ries. How mu<;h less, then, ought we to expect any full demonstration of 

 ihis point in the vessels of vegetables, in every instance so much more minute 

 than those of the more perfect animals, and seldom exceeding, as I have 

 already observed, a three-thousandth part of an inch in diameter! 



It becomes me, however, to confess, that no experiments which have 

 hitherto been made have detected the existence of either motific or sensific 

 fibres themselves in vegetables, although very high degrees of galvanic elec- 

 tricity have for this purpose been applied to the most irritable of them, as the 

 dionaea muscipula, or Venus fly-trap; oxalis sensitiva ; different species of 

 drosera, or sun-dew ; acacias of various kinds, and other mimosas ; and espe- 

 cially the mimosa pudica^ and sensitiva, the common sensitive plants of our 

 green-houses. Humboldt has uniformly failed ; Rafn appears to have suc- 

 ceeded in one or two instances; but his general want of success prevents us 

 from being able to lay any weight on-the single case or two in which he 

 seems to have been more fortunate. 



It should be observed, that the matter of fibrine, or the principle of the 

 muscular fibre, formerly supposed to exist exclusively in animal substances, 

 has lately been detected by M. Vauquelin in vegetables also. Dr. Hales cut 

 off the stems of vines in the spring, and by fixing tubes on the stumps, found 

 that the sap rose in many instances to the height of thirty-five feet. Tubes 

 have been fixed to the large arteries of animals, as near as possible to the 

 heart, in which the blood did not rise higher than nine feet. 



It has long been admitted by botanists in general, that the thorns of plants 

 are abortive branches ; the scales of buds have, in like manner, been regarded 

 as transformed leaves ; and it has lately been conjectured by M. de Candolle, 



* Impatiens balsamina .-—This is the plant recommended by M. Willdenow for this purpose, as afford 

 ing the clearest results. 



t Yet Hales and Duhamel seem to have shown, that in the sap- vessels no valves exist, and that branches 

 imbibe moisture nearly equally at either end. See Thomson's Chemistry, v. 385 ; an assertion, however, 

 opposed by various facts. See also Smith's Introd. p. 57. 60. 



