was general, with the intention of examining whether the motion would return again when they were immersed in water : he has never found, however, the circulation to be restored, no matter how short a time had elapsed since the stoppage, or how low or high the degree of heat had been, at which the stagnation had taken place. This is a strong argument against the probability of a physical cause for the phenomenon. "The physical causes assumed to account for the matter had been various, and he would notice a few.

"Endosmose and exosmose had been considered competent to explain the phenomenon, and he had at one time entertained the same notion; but the idea is untenable, for the circulation goes on equally well in water, and in air (until desiccation is produced), in oil, and in a saccharine solution.

"Others had attempted to account for it on the principle of that epipolic force, which causes two fluids of different densities and miscible materials in contact with each other, to be in a constant state of rotation until they are entirely amalgamated. This, however, assumes the existence of two fluids in the plant; whereas, we have every reason to believe that one only, i. e., that within the cell, is necessary to the production of the circulation. Even if the existence of the two necessary fluids be granted, we have every reason to believe that their action upon each other would be uniform, not fitful and irregular, as we have seen the motions of the chlorophyll to be.

"Electricity has been proved to have no direct agency at all.

"The author was led to consider that the phenomenon in question is due to vital causes, by the following considerations :

"That the circulation is fitful and irregular, varying in rapidity at different points of the same cell. That although it does not ordinarily exist in the valisneria when growing, yet

that it does occasionally in it, and constantly in other plants. That in those parts of the leaf which had been removed from the parent plant, and in which the circulation was general, vitality had not absolutely departed, as one or two of them had been known to grow after the separation.* The effects of certain vegetable poisons in entirely destroying the circulation, while others only affect it a short time, their influence passing away under favourable circumstances, afford strong evidence of its dependence upon vital causes.

"If a sensitive plant were treated in the same way as the valisneria, its irritability would be equally destroyed by prussic acid and opium, and it would be recovered equally when removed from their influence. The vital character of the phenomenon in the one could not be established, as it had been in the former, without allowing it in the latter."

The author then adduced some instances of circulation in the animal world which seemed analagous to that in the valisneria, and which could only be explained by presuming the existence of a vital and unknown force.

"In the chick the area vasculosa is beset with dark aggregated masses; single isolated points then appear; between these, clefts are formed that, by and by, run together and form channels, which unite in meshes with one another; in these channels a clear, colourless, or extremely pale liquid, of a yellow colour, can, by and by, be distinguished in motionthis is the blood. Along with these changes the development of the heat has been adrancing,' &c.; i. e., the motion commenced in the blood independent of the heart.

"Again, in a more advanced state of existence, the phenomenon of circulation has been witnessed independent of a heart. "Mr. Hassall has stated, in his Microscopic Anatomy, that he has witnessed a most regular, and constant circulation, in

*The Rev. T. Dwyer, to whom the slips exhibited at the Society were given, has since informed the author, that one of the green ones has sent forth roots, and begun to exist as an independent plaut, evidently showing that it had retained its vitality.

the capillaries of a frog's tongue, for many hours after it had been separated from the body. Muller states, that in several of the lowest tribes of animals, there are circular currents, similar to those in the chara. Nordmann has observed in the envelope of the 'alcyonella disaphana' small isolated circulations; and Carus has seen similar in the ambulacra of the sea urchin. Ehrenberg has observed circular currents of granules in the medusæ, and in the retractile fibres on the dorsal aspect of the asterias.

"The author has before described motions in different forms of vegetable life, especially in the so-called spores of the conferva glomerata, and need not revert to them again.

Upon a careful review of the arguments, it appears that the great preponderance is in favour of the supposition, that the cause of the motion is a purely vital one. It is true, that motion continuing after the apparent death of the leaf, militates somewhat against this deduction; but it must be borne in mind, that change of colour is not absolute proof that all vitality has departed—and even if it were, the importance of the facts is thrown completely into the shade, by the observation recorded at a previous part, respecting the effects of desiccation.

"After having thus arrived at the vital nature of the phenomenon, all enquiry must for the time close, as the powers of life are as inscrutable in the vegetable as in the animal kingdom."

The author then concluded his paper, by detailing some experiments on the circulation in the hairs of terrestrial plants; showing, that in them stagnation did not take place either in oil or air; but, that immersion in water soon destroyed the motion, by changing the condition and contents of the cell.

In these cases there was no doubt of the vital character of the phenomenon.

that it does occasionally in it, and constantly in other plants. That in those parts of the leaf which had been removed from the parent plant, and in which the circulation was general, vitality had not absolutely departed, as one or two of them had been known to grow after the separation.* The effects of certain vegetable poisons in entirely destroying the circulation, while others only affect it a short time, their influence passing away under favourable circumstances, afford strong evidence of its dependence upon vital causes.

"If a sensitive plant were treated in the same way as the valisneria, its irritability would be equally destroyed by prussic acid and opium, and it would be recovered equally when removed from their influence. The vital character of the phenomenon in the one could not be established, as it had been in the former, without allowing it in the latter."

The author then adduced some instances of circulation in the animal world which seemed analagous to that in the valisneria, and which could only be explained by presuming the existence of a vital and unknown force.

"In the chick the area vasculosa is beset with dark aggregated masses; single isolated points then appear; between these, clefts are formed that, by and by, run together and form channels, which unite in meshes with one another; in these channels a clear, colourless, or extremely pale liquid, of a yellow colour, can, by and by, be distinguished in motionthis is the blood. Along with these changes the development of the heat has been advancing,' &c.; i. e., the motion commenced in the blood independent of the heart.

"Again, in a more advanced state of existence, the phenomenon of circulation has been witnessed independent of a heart. "Mr. Hassall has stated, in his Microscopic Anatomy, that he has witnessed a most regular, and constant circulation, in

The Rev. T. Dwyer, to whom the slips exhibited at the Society were given, has since informed the author, that one of the green ones has sent forth roots, and begun to exist as an independent plaut, evidently showing that it had retained its vitality.

the capillaries of a frog's tongue, for many hours after it had been separated from the body. Muller states, that in several of the lowest tribes of animals, there are circular currents, similar to those in the chara. Nordmann has observed in the envelope of the 'alcyonella disaphana' small isolated circulations; and Carus has seen similar in the ambulacra of the sea urchin. Ehrenberg has observed circular currents of granules in the medusa, and in the retractile fibres on the dorsal aspect of the asterias.

"The author has before described motions in different forms of vegetable life, especially in the so-called spores of the conferva glomerata, and need not revert to them again.

"Upon a careful review of the arguments, it appears that the great preponderance is in favour of the supposition, that the cause of the motion is a purely vital one. It is true, that motion continuing after the apparent death of the leaf, militates somewhat against this deduction; but it must be borne in mind, that change of colour is not absolute proof that all vitality has departed—and even if it were, the importance of the facts is thrown completely into the shade, by the observation recorded at a previous part, respecting the effects of desiccation.

"After having thus arrived at the vital nature of the phenomenon, all enquiry must for the time close, as the powers of life are as inscrutable in the vegetable as in the animal kingdom."

The author then concluded his paper, by detailing some experiments on the circulation in the hairs of terrestrial plants; showing, that in them stagnation did not take place either in oil or air; but, that immersion in water soon destroyed the motion, by changing the condition and contents of the cell.

In these cases there was no doubt of the vital character of the phenomenon.