On the Action of detached Leaves of Plants. By Thomas Andrew Knight, Esq. F.R.S. In a Letter addressed to the Right Hon. Sir Joseph Banks, Bart. G.C.B. P.R.S. Read June 13, 1816. [Phil. Trans. 1816, p. 289.]

Mr. Knight having on a former occasion inferred, from his experiments and observations, that the true sap of trees, from which the living parts are generated, owes its properties to having circulated through the leaves, now adduces other facts, more directly in point, to show that a fluid similar to the true sap actually descends through the leaf-stalks.

A transverse section was made through the bark of a vine, at the middle of the insertion of the leaf-stalk, by passing a slender knife through the stalk, so as to split it for about two thirds of an inch above its insertion.

Another transverse incision of the bark having also been made nearly an inch below, these sections were joined by longitudinal incisions at each end, so that a piece of the bark, half an inch broad and nearly one inch long, could be detached from the stem, still remaining united to the lower half of the split leaf-stalk. Being afterwards protected on all sides from the air by waxed paper, it was found to grow in all its dimensions, and to have thin layers of alburnum deposited upon its interior surface.

In a second experiment, leaves from the potatoe were taken at the period when the tuberous roots were beginning to form, and were planted in pots, under the expectation that these leaves even alone might have power to form tubers. The effect, however, was not exactly as the author had anticipated; but the power was manifested by the production of a conical swelling at the lower part, more than two inches in circumference, apparently similar in composition to a tuber, and retaining life to the following spring.

Leaves of mint, also detached in the same manner, were found to throw out roots, and to continue alive through the winter, assuming the character and hue of those of evergreen trees.

Since it had appeared, from former experiments, that the growth of immature leaves depends upon matter afforded by those already arrived at a state of maturity, Mr. Knight cut off several shoots of a vine, and laying them over basins of water, immersed portions of the larger leaves; and he found that under these circumstances the young leaves continued to grow for upwards of a month, during which they necessarily depended on the larger leaves for their supply of nourishment.

The progress of fruit, likewise, is proved to depend upon the mature leaves; for if these be destroyed, the fruit ceases to grow, and gains nothing in ripeness or flavour: and, accordingly, those trees alone are capable of ripening fruit during winter which retain their leaves at that season, of which the Orange, Lemon, Ivy, and Holly, are familiar examples.

With regard to the period during which the true sap is accumu

lated as store for future growth, and returned from its reservoirs into the circulation, it may be difficult clearly to discover anything certain; but the author has not ceased to prosecute his experiments on the varying density of the alburnum, and other parts of the wood, and on the proportion of moisture which they lose by drying; and he hopes at some future time to lay before the Society his observations, showing how far the durability of the heart wood depends on the period at which a tree is felled.

On the Manufacture of the Sulphute of Magnesia at Monte della Guardia, near Genoa. By H. Holland, M.D. F.R.S. Read June 13, 1816. [Phil. Trans. 1816, p. 294.]

The site of this manufactory is about eight miles N.W. of Genoa, at about 1600 feet above the level of the sea, from which the top of the mountain is five miles distant, and elevated about 2000 feet. The ascent from Sestri is by a deep ravine, the course of a torrent, the eastern side of which is composed of serpentine in vast masses, lying unconformably on primitive schist, and containing talc, steatite, asbestus, and many small veins of pyrites. On the western side of the ravine are mountains of magnesian limestone. In passing to the upper end of this ravine, the stratification of the primitive schist appears mixed with chlorite, slate, and other magnesian minerals, and containing numerous veins or layers of pyrites, both of copper and iron. The substance of these ores is schistose, as well as the rock in which they lie, and they are so intimately mixed with the same magnesian minerals, as to feel unctuous to the touch. These, together with a certain portion of magnesian limestone, are the materials used in the manufacture of the sulphate of magnesia, in an establishment originally set up for converting copper and iron pyrites into sulphates of those metals.

The sulphate of magnesia was at first observed only as an accidental product, but has now become the principal object of the work. For this purpose the pyrites is extracted from the mountain by tunnels, the largest of which is about 200 feet in length, and from 10 to 15 feet wide. The ore is then broken into small pieces, roasted for about ten days, and being then collected in heaps, is kept moist with water for several months, during which the salts are forming. The materials are then lixiviated, and after the liquor has been filtered through sand, the copper is first precipitated by refuse iron, after which a portion of lime, prepared from the magnesian limestone of the adjacent mountain, is added, in order to precipitate the iron, and at the same time to make some addition to the product of sulphate of magnesia.

The circumstance particularly to be attended to in this process, is the proportion of lime employed, which in general does not exceed 4th of the weight of ore. For if this were added in excess, it would occasion the precipitation of the magnesia along with the metals. The whole produce of this manufactory, we are told, does

not exceed 1 cwt. per week; but it is of very good quality, and is used extensively in Italy under the name of Sal Inglese.

On the Formation of Fat in the Intestine of the Tadpole, and on the Use of the Yolk in the Formation of the Embryo in the Egg. By Sir Everard Home, Bart. V.P.R.S. Read May 23, 1816. [Phil. Trans. 1816, p. 301.]

From the smallness of tadpoles in this country, they have not attracted the notice of naturalists so much as their peculiarities deserve. But those of the Rana paradoxa of Surinam being of a much larger size, are fitter subjects for observation. The tadpole of this frog bears so strong a resemblance to a fish, that it is commonly sold as such for the use of the table. But as these are not to be had here in sufficient quantity for examination, the author had recourse to the common tadpole of this country.

This animal, as soon as it leaves the ovum, has ten filaments projecting from the neck on each side, which answer the purpose of gills. In the young shark, while yet in the egg, there are twenty-four similar filaments to answer the same purpose. In the common newt also is a similar apparatus, but the number is only three on each side. In each instance this structure is but temporary, and drops off when the permanent structure of lungs in the frog, and of gills in the shark, is completely formed.

During the growth of the tadpole its abdomen becomes distended, the intestine being then very capacious, and filled throughout its whole extent with a soft substance, that burns with a vegetable smell. Behind the intestine, along the posterior part of the abdomen, is accumulated a quantity of fat of a yellow colour, inclosed in long thin transparent membranous bags. During the conversion of the tadpole into the frog by development of the legs, lungs, and other organs before wanting, the whole of this fatty matter becomes absorbed, in the same manner as the yolk of the hen's egg is taken up during the progressive growth of the young chicken. So that although the egg of the frog differs from that of other animals of the same class in having no yolk, a substance corresponding to it appears to be necessary previous to the formation of bones, and other more solid parts of the perfect frog. For the production of this matter, it is observed that the tadpole is provided with a most uncommon length of intestine, which contracts to one of ordinary size as soon as the full supply of fat is generated.

The author adds the result of various chemical experiments, made by Mr. Hatchett and Mr. Brande on the spawn of the frog, from which it appears, that it is of a nature between gelatin and albumen; that it contains no concrete oil like that of the hen's egg; that the ova of the lizard and snake, and of cartilaginous fishes, have, on the contrary, yolks which do contain a concrete oil, that in its nutritive qualities corresponds to the butyraceous part of milk with which the young of viviparous animals are supported for a certain time after birth.

From these observations, and from the peculiar provision of fat laid up by the tadpole previous to its metamorphosis into the frog, Sir Everard Home is led to consider a certain portion of oil as necessary for the formation of bone, and to observe that the proportion of fat in different ova, corresponds with the greater or less degree of hardness of bone that is about to be produced.

On the Structure of the Crystalline Lens in Fishes and Quadrupeds, as ascertained by its Action on Polarized Light. By David Brewster, LL.D. F.R.S. Lond. and Edin. In a Letter addressed to the Right Hon. Sir Joseph Banks, Bart. G.C.B. P.R.S. Read June 20, 1816. [Phil. Trans. 1816, p. 311.]

The author having found that in many instances depolarization depends upon variations of density in the bodies through which it is transmitted, concluded that corresponding effects would be produced by the crystalline lens of the eye, which is well known to increase in density towards the centre.

By immersing the crystalline lens of a cod in Canada balsam, the refraction at its exterior surface was so far removed, that the effects of its internal texture could be examined independent of its external spherical form. Under these circumstances, when it was exposed to polarized light, with its axis of vision parallel to the beam of light, it exhibited three concentric circles of light separated by two dark circles, and intersected by a black cross so as to be divided into twelve lumincus sectors. By varying the inclination of the axis, these appearances varied in a manner that can scarcely be described without the assistance of the drawings which accompany this paper.

By removing successively the capsule and outer portions of the lens, the exterior circle of light was first obliterated; and then the second disappeared, so that ultimately there remained only the central light intersected by a black cross.

On examination of the variation of tints of colours produced by the combined effect of the crystalline with a plate of sulphate of lime, it appeared to the author that the central nucleus, and an exterior spherical coat, are in a state of dilation, while the intermediate coats are in a state of contraction.

In the crystallines of sheep and oxen, the author observed a correspondent texture; but in these there appeared only one series of luminous sectors.

By examination of the cornea also, Dr. Brewster found a texture similar to that of the nucleus of the crystalline, both in fish and quadrupeds; but the sclerotic coat has merely a confused power of depolarization, similar to that of a mass of crushed jelly of isinglass, a property which does not really belong to its whole substance, but solely to a thin membrane that covers it externally.

From these experiments Dr. Brewster infers, that all the parts of the crystalline of fishes correspondent to the two dark concentric circles, exercise no action upon polarized light; that a central nu

cleus and an external spherical shell are in a state of dilatation, and that a shell intermediate between them is in a state of contraction; that its structure and optical properties are not alike in all directions, but have reference to the axis of vision; and that its peculiar structure probably is necessary for correcting spherical aberration.

Some farther Account of the Fossil Remains of an Animal, of which a Description was given to the Society in 1814. By Sir Everard Home, Bart. V.P.R.S. Read June 13, 1816. [Phil. Trans. 1816, p. 318.]

The present descriptions are taken from specimens in the collection of Mr. Buckland of Oxford, and Mr. Johnson of Bristol, and are thought to determine the class to which this animal belongs.

The structure of the vertebræ, as shown in the author's former paper, made it evident that the progressive motion of the animal resembled that of fishes; but at that time neither the scapula in its perfect state had been seen, nor had the bones of the pectoral fin been found, which now make it clear that all the bones correspond with those of fishes, but differ essentially from those of land animals.

In all animals that breathe by means of lungs, the ribs are articulated both to the bodies and to the transverse processes of the vertebræ, so as to admit of expansion of the chest; but the ribs of fishes which solely give defence to the viscera, have only one insertion, being connected solely with the bodies of the vertebræ, midway between their two articulating surfaces, so as not to interfere with the motion of the vertebræ on each other, as is the case in land animals. The author observes, that the ribs in this animal are placed in all respects like those of fish.

In the whale tribe the scapula and bones of the fore fin resemble those of the crocodile, and they bear a close analogy to those of land animals in general; but in this animal these bones, it is observed, resemble those of the shark.

It is remarked also, that the bones in the young state have epiphyses, as is the case with the bones of fish generally. The ribs also appear to have been soft like those of fish, as we may judge from the grooved or fluted form, they have assumed by compression.

But though, from consideration of all these circumstances, Sir Everard Home has no doubt that this animal was a fish, he admits that the long projecting snout and conical teeth show a marked difference between this animal and any now in existence, and may occasion a difficulty in arranging it with any class of known animals.

Farther Observations on the Feet of Animals whose progressive Motion can be carried on against Gravity. By Sir Everard Home, Bart. V.P.R.S. Read June 27, 1816. [Phil. Trans. 1816, p. 322.] Since the author's former observations on this subject were communicated to the Society, he has been enabled, by the assistance of