On the Sap of Trees. By AND. KNIGHT, Esq.-[1805.]

THE sap in trees in an inspissated state, or some concrete matter deposited by it, exists during the winter in the alburnum or sapwood, and from this fluid or substance, dissolved in the ascending aqueous sap, is derived the matter which enters into the composition of the new leaves in the spring, and thus furnishes those organs which were not wanted during the winter, but which are essential to the further progress of vegetation. Hence, the superiority of winter-felled wood, which has generally been attributed to the absence of the sap at that season, is owing to the substance that has been added to it instead of taken from it.

Bulbous and tuberous roots are almost wholly generated after the leaves and stems of the plants to which they belong have attained their full growth; hence, the produce of meadows is greatly increased when the herbage of the preceding year remained to perform its proper office till the end of the autumn, on ground which had been mowed early in the summer. On this account Mr. Knight infers, that the leaves both of trees and herbaceous plants are alike employed during the latter part of summer, in the preparation of matter calculated to afford food to the expanding buds and blossoms of the succeeding spring, and to enter into the composition of new organs of assimilation. In proof of this hypothesis Mr. Knight made many experiments, an account of which he has, by means of this letter, laid before the Royal Society. The evidence that bulbous and tuberous rooted plants contain matter within themselves is decisive; for they vegetate even in dry rooms on the approach of spring; and many bulbous rooted plants produce their leaves and flowers with nearly the same vigour by the application of water only, as they do when growing in the best mould. The water probably acts only by dissolving the matter prepared and deposited in the preceding year, and hence the root becomes exhausted and spoiled; and it has been found, that the leaves and flowers and roots of such plants afforded no more carbon than exist in bulbous roots of the same weight, the leaves and flowers of which had never expanded.

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From experiments made with care, Mr. Knight infers, that the reservoir of matter, deposited in the alburnum, is not wholly exhausted in the succeeding spring, from which circumstance he accounts for the several successions of leaves and buds which trees are capable of producing, when those previously protruded have been destroyed by insects or other

causes; and for the luxuriant shoots which often spring from the trunks of the trees whose branches have been long in a state of decay. He thinks, that the alburnum remains unemployed in some cases during several successive years, since it is not probable that it can be employed by trees, which, after having been transplanted, produce very few leaves, or by those which produce neither blossoms nor fruit. In the year 1802, Mr. Knight cut off in the winter all the branches of a pear-tree, supposed to be nearly 200 years old, and whose extremities were generally dead; he pared off, at the same time, all the lifeless external bark. No marks of vegetation appeared in the following spring; but in July numerous buds penetrated through the bark, and in the autumn every part was covered with shoots about two feet in length. The number of leaves and branches appeared to exceed the whole of those which the tree had borne the three preceding seasons, which could scarcely have been wholly prepared by the scanty vegetation and foliage of the preceding year.

As inferences from his experiments, Mr. Knight concludes that the fluid which enters into and circulates through the leaves of plants, as the blood through the lungs of animals, consists of a mixture of the true sap or blood of the plant, with matter more recently absorbed and less perfectly assimilated. It is probable that the true sap undergoes a considerable change on its mixture with the ascending aqueous sap; and that the saccharine matter, existing in the ascending sap, is not wholly derived from the fluid which had circulated through the leaf in the preceding year, but that it is generated by a process similar to that of the germination of seeds, and that the same process is always going forward during the spring and summer, as long as the tree continues to generate new organs. But towards the conclusion of the summer, the true sap simply accumulates in the alburnum, and thus adds to the specific gravity of winter-felled wood, and increases the quantity of its extractive matter. And he adds, " If subsequent experiments prove that the true sap descends through the alburnum," as he suspects to be the case, "it will be easy to point out the cause why trees continue to vegetate after all communication between the leaves and roots, through the bark, has been intercepted; and why some portion of alburnous matter is in the trees generated below incision through the bark."

On the Direction of the Sun and Solar System. By Dr.

HERSCHEL.

THE learned astronomer conceived, more than twenty years ago, that it was highly probable there was a motion of the sun and solar system towards a Herculis; and he says, the reasons which were in 1783 pointed out for introducing a solar motion, will now be much strengthened by other considerations. He conceives that the motion of the sun and solar system will account for the apparent motions of the larger fixed stars upon much the easiest principles. Thus, by admitting a motion of the sun towards Herculis, the annual motions of six stars, viz., Sirius, Arcturus, Capella, Lyra, Aldebaran, Procyon, may be reduced to little more than 2", whereas the sum of them would be 5".3537; and, by another table, founded on a calculation of the angles, and the least quantities of real motion of the same six stars, it appears that the annual proper motion of the stars may be reduced to 1".4594, which is 0".7655 less than the sum in the former case.

On the singular Figure of the Planet Saturn. By Dr. HERSCHEL.[1805.]

THERE is not, perhaps, another object in the heavens that presents us with such a variety of extraordinary phenomena as the planet Saturn. A magnificent globe, encompassed by a stupendous double ring, attended by seven satellites, ornamented with equatorial belts, compressed at the poles; turning upon its axis, mutually eclipsing its ring and satellites, and eclipsed by them; the most distant of the rings also turning upon its axis, and the same taking place with the farthest of the satellites; all the parts of the system of Saturn 'occasionally reflecting light to each other, the rings and moons illuminating the nights of the Saturnian, the globes and satellites enlightening the dark parts of the rings; and the planet and rings throwing back the sun's beams upon the moons, when they are deprived of them at the time of conjunction.

Besides these circumstances, which appear to leave hardly any room for addition, there is yet a singularity left, which distinguishes the figure of Saturn from that of all the other planets. It is flattened at the poles, but the spheroid that would arise from this flattening is modified by some other cause, which Dr. H. supposes to be the attraction of the ring. It resembles a parallelogram, one side of which is the equa

torial, the other the polar diameter, with the four corners rounded off, so as to leave both the equatorial and polar regions flatter than they would be in a regular spheroidical figure.

On the Reproduction of Buds. By Mr. KNIGHT.-[1805.] EVERY tree, in the ordinary course of its growth, generates in each season those buds which expand in the succeeding spring, and the buds thus generated contain, in many instances, the whole leaves which appear in the following summer. But if these buds be destroyed in the winter, or early part of the spring, other buds, in many species of trees, are generated, which in every respect perform the office of those which previously existed, except that they never afford fruit or blossoms.

He then proceeds to mention different theories to account for this; and, as his own opinion, he says, that the buds neither spring from the medulla nor the bark, but are generated by central vessels, which spring from the lateral orifices of the alburnous tubes. The practicability of propagating some plants from their leaves may seem to stand in opposi tion to this hypothesis; but the central vessel is always a component part of the leaf, and from it the bud and young plant probably originate.

Mr. K. thinks that few seeds contain less than three buds, one of which only, except in cases of accident, germinates. Some seeds contain a much greater number. The seed of the peach appears to be provided with ten or twelve leaves, each of which probably covers the rudiment of a bud, and the seeds, like the buds of the horse-chesnut, contain all the leaves, and apparently all the buds, of the succeeding year.

Differences in the Magnetic Needle on board His Majesty's Ship the Investigator, arising from an Alteration in the Direction of the Ship's Head. By Captain FLINDErs.

THERE was a difference in the direction of the magnetic needle when the ship's head pointed to the east, and when it was directed westward.

This difference was easterly when the ship's head was west, and westerly when it was east.

When the ship's head was north or south, the needle took the same direction, or nearly so, that it would on shore, and showed a variation from the true meridian.

The error in variation was nearly proportionate to the

number of points which the ship's head was from north or south.

Hence the captain supposes, 1. An attractive power of the different bodies in a ship, which are capable of affecting the compass, to be collected into something like a focal point or centre of gravity, and this point is nearly in the centre of the ship, where the iron shot are deposited. 2. He supposes this point to be endued with the same kind of attraction as the pole of the hemisphere where the ship is: consequently, in New Holland, the south-end of the needle would be attracted by it, and the north end repelled. 3. That the attractive power of this point is sufficiently strong in a ship of war to interfere with the action of the magnetic poles upon a compass placed upon or in the binnacle.

On the Arrangment and Mechanical Action of the Muscles of Fishes. By ANTHONY CARLISLE, Esq.-[1806.]

THE muscles of fishes are of a very different construction from those of the other natural classes. The medium in which these animals reside, the form of their bodies, and the instruments employed for their progressive motion, give them a character peculiarly distinct from the rest of the creation. The frame-work of bones or cartilages is simple; the limbs are not formed for complicated motions; and the proportion of muscular flesh is remarkably large. The muscles of fishes have no tendinous chords, their insertions being always fleshy. There are, however, semi-transparent pearly tendons placed between the plates of the muscles, which give origin to a series of short muscular fibres passing nearly at right angles between the surfaces of the adjoining plates.

The motion of a round-shaped fish, independent of its fins, is simple: it is chiefly effected by the lateral flexure of the spine and tail, upon which the great mass of its muscular flesh is employed, whilst the fins are moved by small muscles, and those, from their position, comparatively but of little power.

Mr. C. first describes the fins, the purposes to which they are employed, and the muscles attached to them; and then, in order to ascertain the effect of the fins on the motions of fishes, he performed a variety of experiments. A number of living dace, of an equal size, were put into a large vessel of The pectoral fins of one of these were cut off, and it was replaced with the others; its progressive motions were not at all impeded, but the head inclined downwards, and

water.