48 



HISTORY OF THE VEGKTABLK KINGDOM. 



he found tliat the latter rose sometimes half an 

 inch in half an hour, sometimes three inches in 

 one hour, and sometimes four inches in three 

 hours. 



From the ohservations and experiments of 

 Professor Amici, it would appear that the fluids 

 contained in the vessels, or in the areolse of the 

 cellular tissue of plants, move and circulate in 

 each of these vessels or cells, quite independently 

 of the manner in which they move in the others. 

 Each cavity, he says, constitutes a distinct organ, 

 and in its interior the fluid moves in a circulat- 

 ing manner, independentlj' of the particular 

 circulation which takes place in each of the 

 adjacent cavities. It was chiefly on Chara vul- 

 garis, Ch. fexilis, and Caulinia fragilis, aquatic 

 plants whose organization is more easily per- 

 ceived on account of the transparency of their 

 elementary piu-ts, that Professor Amici made his 

 ohservations. The motion of the fluid in each 

 cavity of the cellular tissue, or in each vessel, 

 may be distinctly perceived, on account of the 

 solid particles which float in the fluid. These 

 particles, which are globules of extreme minute- 

 ness, and sometimes of a very decided green 

 tint, are seen ascending along one of the walls 

 of the cavity, and, on arriving at the horizontal 

 partition which separates the cell from the one 

 above it, clianging their direction, and following 

 a horizontal course until they reach the opposite 

 wall, when they descend along it to its lower 

 part, where their course again becomes horizon- 

 tal ; after which they recommence the same 

 route. In the same vessel there are thus always 

 four different currents, an ascending, a descending, 

 and two horizontal ones, in opposite directions. 

 It is very remarkable that the direction of the 

 motion in each vessel does not seem to have any 

 connection with that which takes place in the 

 neighbouring tubes. Thus sometimes two vessels 

 in mutual contact present the same motion, while, 

 in those which suiTound them, a directly opposite 

 motion is observed in the fluids. 



The same observer has also remarked, that no 

 globule is seen passing from one cavity into 

 another. " However," says he, " I do not pre- 

 tend to maintain tliat the fluid contained in a 

 vessel, does not, when circumstances require it, 

 penetrate into the neighbouring vessels. I am 

 even persuaded that this transfusion is necessary 

 for the development of the plant ; })ut it is only 

 the most fluid and subtile part of the juice that 

 can penetrate through the membrane invisibly, 

 by passing through holes which the eye, assisted 

 by the microscope, is unable to perceive." 



Some have attributed the cause of this inde- 

 pendent motion of the fluid, to the instability 

 possessed by the membrane of whicli the tubes 

 are formed. Professor Amici is not of this 

 opinion ; but thinks he recognises the moving 

 power of the fluid in the small green or trans- 



parent grains lining the walls of the tubes where 

 they are disposed in rows, and whicli, by an 

 action similar to that of the voltaic piles, produce 

 the motion of the fluid. These green grains are 

 evidently the same as those which Dutrochet 

 considers as the nervous system of vegetables. 



But what is the cause of this ascent of the 

 sap ? How can that fluid lise from the roots to 

 the upper part of the stem? It may well be 

 supposed that each of the older physiologists 

 must have had an opinion of his own to account 

 for this surprising plienomenon. 



Grew attributed it to the action of the utricles. 

 That author, who considered the vegetable tissue 

 as formed of small utricles, placed in juxta-posi- 

 tion, one above another, and all communicating 

 together, thought that when the sap had once 

 entered into the lower utricles, they contracted 

 upon themselves, and pushed it into those im- 

 mediately above ; and that, by this mechanism, 

 the sap at length reached the summit of the 

 plant. Malpighi, on the other hand, attributed 

 the ascent of the sap to its alternate rarefaction 

 and condensation by heat. De La Hire, who 

 supposed the sap-vessels to be furnished with 

 valves, like the veins of animals, thought that it 

 depended upon this arrangement. Perault im 

 agined it to lie produced by a kind of fermentation. 

 Lastly, many persons have compared the pro- 

 gress of thesap in the vegetable tissue, to theascent 

 of fluids in capillary tubes. But it will readily 

 be seen that such hypotheses are insufficient to 

 account for the phenomena in question. If they 

 were owing to the capillarity of the sap-vessels, 

 their action would necessarily be independent of 

 external circumstances, and even of the life of 

 the plant; but this is not the case. Every 

 person knows that the sap no longer circulates 

 in a plant deprived of life. Life has therefore a 

 direct and powerful action upon the exercise of 

 this function. In the suction performed by the 

 roots in the soil, a peculiar vital power has been 

 admitted, on which depend all the phenomena 

 of vegetables, and which fonns the distinctive 

 character of living beings, and withdraws them 

 from the influence of physical and chemical 

 agents ; this power has also been resorted to for 

 explaining the progress of the sap. In short, 

 if all the phenomena of vegetation were produced 

 by the action of mechanical or chemical agents 

 alone, by what characters could we distinguish 

 vegetables from inorganic objects? We must 

 therefore admit in vegetables, as in animals, a 

 peculiar vital power which influences all their 

 functions. But although this vital power be 

 the agent by which the ascent of the sap is pro- 

 duced, certain internal and external causes may 

 facilitate the exercise of this phenomenon. 

 Among the external causes are to be ranked 

 temperature, and the influence of light and 

 electricity. It is generally known that a high 



