leled to the circulation of the blood. The blood is impelled through every part of the body by no mechanical attraction or chemical affinity; but by a principle, sui generis, connected with animal life, and which, though its action may be increased by stimulants, and diminished by narcotics, cannot be communicated by any exertion of human power. The analogy between vegetable and animal life has certainly in some instances been carried beyond the bounds of sober reason, but no one can refuse assent to the existence of a connexion between these two orders of being, indicating a common principle in their organization. The circulation of the blood, therefore, produced by the irritability of the heart, leads us to ascribe the circulation of the sap to a similar organization in the vegetable; and as the examination of the sap vessels in trees does furnish evidence of a construction suited to such a purpose, we have good reason to conclude that this is indeed the true theory of that phenomenon.

The origin of that prejudice which would lead us to ascribe to the circulation of the sap the perpendicular growth of the vegetable will be found in the inaccuracy of the expression ascent of the sap. We now see that, instead of concluding that the germen is forced upwards by the ascending sap, we have better reasons to conclude that the sap ascends, because the plant stands perpendicular. Being absorbed by the roots, its course, if it flows at all, is necessarily upwards in an upright stem. But it flows in all directions, and with equal force in a trailing as in an upright plant. Like the circulation of the blood, which was destined to proceed with an equal course, unaffected by the position of the animal, the flow of the sap, intended to nourish all the parts of the plant, was made to depend on a principle altogether unconnected with those laws which, however powerful or extensive in their operations, are all essentially connected with the centre of gravity. Instead of ascent, therefore, we ought to adopt the expression circulation of the sap; and by the introduction of a term implying an indefinite direction, we shall extricate the question from that confusion which so invariably results from inaccurate descriptive expressions.

But if there be no principle as yet discovered to which, by an internal upward pressure, we can ascribe the full solution of the problem, the conviction that the cause is still to be found in the ascent, or descent of something connected with the plant, leads us to examine the external operations of vegetation, and in particular the constant and copious evaporation which seems essential to the existence of that process.

The quantity of water which is absorbed and evaporated by diffe rent plants has been the subject of many experiments. It has been gravely stated that the improvements in agriculture, by increasing the quantity of vegetables in this island, have so much increased the quantity of vapour as to have materially deteriorated the climate. Without adopting such an unpleasant opinion as this, we may safely credit the statements of well-informed naturalists when, from their

experiments, they inform us that, on an average, vegetables evaporate daily a quantity of water equal to half their weight. Spearmint was found to evaporate its own weight; and a cabbage plant weighing 1 lb. 9 oz. perspired 1 lb. 3 oz. It is scarcely to be doubted that water, which contains two of the elemental ingredients of vegetables, viz. oxygen and hydrogen, does by decomposition furnish nourishment to the plant; but its principal office in the progress of vegetation seems to be to serve as a menstruum for enabling the more fixed elements, carbon, lime, phosphorus, &c. to be imbibed by the roots, and circulated by the other organs. Having accomplished this important service, it unites with the excess of caloric, by which it is converted into vapour; and each lingering gaseous particle, separating with difficulty from its former companion, communicates to every part of the plant an upright direction, in which position it is permanently fixed by the formation and increasing inflexibility of the woody fibre.

It may appear surprising that such a quantity of water should be evaporated from vegetables, whilst their temperature remains not much higher than that of the surrounding atmosphere; but it is to this evaporation we must ascribe the low temperature which the plant preserves in the midst of circumstances calculated to raise it to a much higher degree. These circumstances have been developed by that ingenious naturalist Mr. Daniel Ellis, who has proved that during vegetation in all stages there is a combination of oxygen and carbon," the formation of carbonic acid being the universal law of living or organized bodies, and seeming to be necessary to their life." When the oxygen thus combines, it parts with its caloric; and from experiment it has been found that the caloric evolved during the formation of 30 cubic inches of carbonic acidgas will melt 1 oz. of ice. That a large quantity of carbonic acid gas is daily formed from vegetables, will at once be apparent when it is recollected that, in consequence of the absorption of oxygen by this process, independent of what is formed from the decomposition of water, the presence of a few plants in a room, notwith standing the supply from the ordinary circulating currents, soon renders the air unfit for respiration, and has not unfrequently been the cause of death. The heat thus produced would certainly be destructive of the plant, were it not carried off by the vapour; so that in the vegetable kingdom we find the same beautiful provision which, in the respiration of animals, protects the vital parts from the too powerful action of caloric.

We may hesitate, notwithstanding, to admit evaporation as a cause adequate to produce such an effect as the perpendicular growth of plants, though it is a step gained in our progress if it be admitted that in any degree it has that tendency. But we may feel re-assured, when we recollect that not only has evaporation the effect of producing buoyancy, in the particles adhering to the vapour; but that it is the only cause known connected with vegetation, which does certainly operate to produce such buoyancy. It

becomes us, therefore, to examine minutely all the circumstances connected with the action of this centrifugal force, as they regard parts of the plant on which it acts, and the manner in which its force is exerted.

the

1. The process of evaporation goes on in every part of the plant, though chiefly in the tender parts, the young shoot, and the leaves. The bud, indeed, almost always protrudes the leaves first, and in many plants the leaves continue for a long time to envelope the stem. It must, therefore, be held that almost every particle of a plant, and particularly those particles at the top of the plumula, which are most soft and pliant, are exposed to the action of that centrifugal force, which is produced by the conversion of the particles of water attached to them, into gaseous vapour or steam; and therefore the effect does not depend altogether on the quantity evaporated in a given time, but on the quantity adhering to the plant, and the existing temperature by which the buoyancy of the gas is regulated.

2. We must contemplate each integrant particle of a plant to which a particle of gas adheres, as supported by its cohesion to the contiguous particles by which it is surrounded; so that, independently of any buoyancy derived from its connexion with the gas, it would hang, not downwards, but in a direction more or less inclined, according to the force with which it coheres to the contiguous particles. To the particles, in these circumstances, we have to apply the influence of the ascending vapour. Possessed of considerable buoyancy, or centrifugal force itself, the particle of vapour, whilst it continues to adhere to the particle of the plant, must communicate to it a portion of that buoyancy.

But, 3dly, The operation of this force in raising the particle of the plant to an upright position, must have the advantage of a lever power. The cohesion of the particles of the plant may be resolved into a succession of attractions from the centre to the surface of the stem. Each radius of this circle may be considered as a lever, having the central point as a fulcrum, or rather each particle in succession, may be considered as thus acted upon, the fulcrum of each being that point where the cohesive power is greatest, and which must always be the point nearest the centre. Even in the leaves something of this effect of cohesion will be found; for the footstalk of the leaf serves as its support, and as a medium by which any buoyancy produced in the leaf is immediately communicated to the twig or the stem.

Looking to each particle as thus acted upon, by a force which, though weak, is incessant in its operation; and recollecting what a small force is required to give perpendicularity to even a considerable weight, when supported at no great angle from the perpendicular, we have no reason to conclude that the cause now assigned must under any circumstances of the plant be inadequate to the effect. It is evident from Mr. Knight's experiment with the horizontal wheel that the circumstance of the centrifugal force

being directed only to particles maintained in certain positions by other causes, is very material to the present question. The force to and from the centre produced by the revolutions of the wheel would not have been sufficient to have sustained one twentieth part of the weight of the plants, either roots or germens; but these being supported otherwise, by their coherence to the parts resting on the wheel, even when the shoots at both ends far outstretched the limits of immediate support, the forces generated by the motion were sufficient to sustain the protrusions. It is not to be doubted that the controuling force in that experiment was that produced by the circular motion, which so distinctly arranged the parts of the plants in that position, which corresponded with their respective gravities. But it must be recollected that one effect of the revolutions of the wheel was to create a little atmosphere for itself, all the parts of which would be affected in their centripetal and centifugal forces. The direction of the buoyant gases, therefore, and the effects produced by them, would share the common lot, and have their tendency to ascend or descend in lines perpendicular to the centre of the wheel.

Another instance of the perpendicular elevation of heavy bodies by a force insufficient to sustain a single particle of these bodies, when applied to it in an individual isolated state, may be found in the tides. The moon's attraction is altogether inadequate to counterbalance the gravity of a particle of water, or to prevent its falling to the ground, yet, when it is so applied that one particle rests upon, and to a certain extent is thus supported by other particles, the attraction of the moon is found to be sufficient to sustain a column of water 10 feet high. Whilst we thus see the moon's attraction, which is not to be compared to the buoyancy of gaseous vapour, producing an effect which in the aggregate excites our wonder and admiration, is it too much to believe that, by communicating a part of its buoyancy to the individual particles to which it adheres, the constant evaporation which proceeds from a plant gives to it the tendency to perpendicularity.

Although I have thus ventured to suggest a principle for the solution of the question why vegetables grow upward, I am far from affirming that my opinion has been established by proof. This much, however, appears demonstrable, that evaporation goes on in all living plants with a never-ceasing activity, and that evaporation must, from its nature, communicate buoyancy, or a tendency to perpendicular growth. This buoyancy is the effect of that law of resisted attraction which produces the ascent of a balloon, the rise of water in a pump, and, as I have before stated, the antilunar tide. It is, indeed, the only cause known in nature which produces a direct centrifugal force, as the simple attraction on which it depends is the only known cause which produces a direct descent towards the centre. Whilst, therefore, I admit that much light must be thrown on this subject before we can have an accurate knowledge of the precise mode in which perpendicularity is pro

duced; yet it appears to me that we have sufficient grounds for concluding that it is effected by the operation of buoyant gases.

Having arrived at this conclusion, it is almost impossible to withdraw the mind from contemplating, or to contemplate without admiring, the various combinations dependant on the law of gravityso vast in their extent, yet so minute in their application. When the Author of the Sacred Volume wishes to impart a sublime idea of infinite power, he tells us that God said, "Let there be light, and there was light." To the philosophic mind, which contemplates that mighty influence which binds the spheres, that universality which pervades all nature, and that wonderful adaptation to almost every varied purpose of utility, it must appear that there was a display of infinite wisdom equally sublime when God said, "Let matter gravitate."

ARTICLE VII.

A Comparison of Albumen with Gluten. By H. F. Link,*

FOURCROY first remarked the presence of albumen in vegetables. The expressed juice of cresses, cabbage, scurvy grass, deposited, on standing, a greenish substance, which, when boiled, precipitated a yellowish-grey flocky matter very similar to animal albumen. Afterwards albumen was detected in a variety of vegetable bodies. Vauquelin found it in the sap of the carica papaya, Einhof in potatoes, Schrader in cabbage, Grotthus in the pollen of tulips, &c.; not to mention the observations made during the preparation of sugar from beet. From all this it appears indisputable that a substance is found in plants similar to animal albumen. Proust alone has hesitated about applying this name to vegetable albumen, and considered the matter as at least very much mixed with gluten.

All that is precipitated from the sap of plants by boiling in flocks always appeared to me so similar to gluten, that I have not been able to prevail on myself to consider it as a peculiar substance. There is, indeed, this difference, that the former substance is found dissolved in the sap of plants, and is only brought into a solid state by heat, while the gluten exists already in a solid state in wheat flour. But this is not sufficient to constitute distinct species. We can only say that in wheat flour the same substance occurs in a solid state which is found liquid and in solution in the sap of cabbage. I consider it, therefore, as necessary to compare coagulated albumen with the gluten of plants, in order to determine whether the albumen of plants bears the greater resemblance to animal albumen

* Translated from Schweigger's Journal, vol. xiv. p. 294, October, 1815.