Description of the Pausus. Doctor Adam Afzelius. This genus does not exist in the twelfth edition of the Systema Naturæ, but made its first appearance in a dissertation published at Upsal, by Linnæus, in the year 1775. At that period only one species was known. In the year 1796, Dr. Adam Afzelius, then residing at the British settlement at Sierra Leona, discovered a second, and has described both with elaborate exactness in a paper on this genus, published in the fourth volume of the Transactions of the Linnean Society of London. To this paper nothing can be objected but its extreme prolixity. I shall therefore take the liberty of here reducing it within reasonable compass. The etymology of the name Dr. Afzelius imagines to be from the Greek Tavos, signifying a pause, cessation, or rest; for Linnæus, now old and infirm, and sinking under the weight of age and labour, saw no probability of continuing any longer his career of glory. He might therefore be supposed to say "hic meta laborum," as it in re ality proved at least with regard to insects; pausus being the last he ever described. dilated and deepened before, and By encompassed on the sides with diverging and outwardly declining lobes; being rounded at the top, and provided with shining hairs of a fulvous colour and beat inwards: the elytra are without dots, and rather longer than the abdomen : the under or real wings are sooty, and without the least glossiness: the abdomen has the terminal segment very retuse, and the margin of the next before it is visibly raised; the pivots of the antennæ are black, very bright, and at first sight might be easily taken for eyes; the under joint is furnished with a wart on the inner margin of the top, covered with papillary or cartilaginous hairs: the upper joint or clava is dotted, much larger than the head, and of th shape of an oblong spheroid, being rounded in front and com pressed, with the carina raised into a sharp edge, provided on the ver tex with four tubercles set in a row and tipped with hairs, and elongated behind into an obtuse tube, laterally compressed, above depres sed, and underneath having a knob, which, in moving, touches the bundle of hairs on the top of the under joint the pedicle is long and crooked, its upper part being broader, compressed, and keeled in front the interior palpi are of 3 lanceolate-oblong shape, and for nished with very minute hinges: the mandibles have small hinges: and the inferior sheath is much larger than the superior: the hind-legs are a little shorter than the others: the joints of the tarsi are difficultly distinguished. This rare insect is a native of Banana island, and Sierra Leona in Africa. Its colour is a blackish brown. He named the insect pausus microcephalus. The head The head is uncommonly small; the thorax broader than the head, and very uneven, the two parts being entirely separated by a transverse furrow; the foremost division is elevated into a sharp ridge resembling a collar, and the hindmost is depressed or cut out in the middle into a cavity, which is obtuse behind, The The second species, or pausus sphærocerus, is thus described by Dr. Afzelius. one "I have been in Africa almost "three years before I happened to "meet with this remarkable little "insect; and then it was quite ac"cidentally. There was a house "building for the governor, on an "eminence called Thornton Hill, at "the South end of Free-Town, in "Sierra Leona; and in the begin"ning of the year 1795 several "apartments having been got ready, "so as to be habitable, one of them "was allotted to me, and I remov"ed into it in the end of the month “of January. I had not resided "there many days, when "evening, having just lighted my "candle and begun to write, I ob"served something dropping down "from the ceiling before me upon "the table; which, from its singular 66 appearance, attracted my par"ticular attention. It remained for "a little while quite immoveable, "as if stunned or frightened, but "began soon to crawl very slowly "and steadily. I then caught it, and, "from the remembrance I had of "the Linnæan species, I directly "took it for a non descript of this "genus. Some few days after, "coming into my room from supper, "with a light in my hand, and "having put it upon the table, "there instantly fell another down "from the ceiling. The third I "was favoured with by the then "governor, Mr. Dawes, who in"formed me that it had dropped "down before him on the table, "just when he had entered his "room, and was going to write. "The other three, which I after"wards collected, were also got 66 upon similar occasions, and from ment, the globes of the antennæ, "like two lanthorns, spreading a "dim phosphoric light. This "singular phenomenon raised my 66 curiosity, and, after having ex"amined it several times that night, "I resolved to repeat my researches "the following day. But the "animal, being exhausted, died be"fore the morning, and the light "disappeared. And afterwards, "not being able to find any more specimens, I was prevented from "ascertaining the fact by reiterated "experiments at different times; which I therefore must recommend "to other naturalists who may have "an opportunity of visiting Sierra "Leona, requesting that they would "particularly enquire into this "curious circumstance. I shall "now only add some few remarks, "shewing in what manner this new "species differs from the old one. "Not being quite so broad, it looks as if it were longer, and more " cylindrical: it is also of a lighter or chesnut colour, and all over "very glossy. The head is larger, but its annular base part smaller, " and contracted: it is furnished "with a little horn in the middle, "between the eyes, which is straight, the eyes are "conic, and tipped with a tuft of bles an inflated bladder, being "almost pellucid, and of a light flesh-colour: the keel is nothing "more than a raised line, finish❝ing on the vertex in only one "chesnut-brown tubercle covered "with cartilaginous hairs: behind there is a little conical shining "hook, of the same colour and with "the same sort of hairs bending "outwardly, being of equal length "with the horn on the head, but "narrower the pedicle is short, "straight and cylindrical. The in"terior palpi, furnished with very "visible hinges, are a little thicker "towards the top, but look, in "some directions, as if they were filiform: the mandibles have large hinges, and the superior sheath "almost as long as the inferior one, "and nearly cylindrical. The tho гах is of the same breadth with "the head, and not very uneven, "the two parts being separated by a furrow only on the sides and Moderneath, the foremost above and on the sides, resembling an "annular segment, and the hinder "one impressed in the middle with "a mark somewhat like two small diverging wings, of a blackish "silvery colour. The elytra are "shorter than the abdomen, and "minately punctated: the under "wings are of a shining and change"able violaceous colour, and not 66 very dark: the abdomen has the "terminal segment a little conve " and in the female more so than in "the male: underneath, the third "and last segments are darker than "the others, the legs are all of equat "length; the tarsi longer than "those of the pausus microcepha lus, and have both the joints and "the claws much more distinct.” Account of some Experiments on the My dear sir, In a memoir which I had the honour to present to you two years ago, I related some experiments on trees, from which I inferred, that their sap, having been absorbed by the bark of the root, the trunk and the branches; that it passes through what are there called the central vessels, into the succulent part of the annual shoot, the leaf-stalk, and the leaf; and that it returns to the bark, through the returning vessels The principal of the leaf-stalk. object of this paper is, to point out the causes of the descent of the sap through the bark, and the conse quent formation of wood. These causes appear to be gravita tion, motion, communicated by windy winds, or other agents, capillary attraction, and, probably, something in the conformation of the vessels themselves, which renders them better calculated to carry fluids in one direction than in another. I shall begin with a few observations on the leaf, from which all the descending fluids in the tree appear to be derived. This organ has much engaged the attention of naturalists, particularly of M. Bonnet, but their experiments have chiefly been made on leaves severed from the tree; and, therefore, whatever conclusions have been drawn, stand on very questionable ground. The efforts which plants always make to turn the upper surfaces of their leaves to the light, have with reason induced naturalists to conclude, that each surface has a total distinct office; and the following experiments tend strongly to support that conclusion. I placed a small piece of plate glass under a large vine leaf, with its surface nearly parallel with that of the leaf, and as soon as the glass had acquired the temperature of the house in which the vine grew, I brought the under surface of the leaf into contact with it, by means of a silk thread and a small wire, adapted to its form and size. Having retained the leaf in this position one minute, I removed it, and found the surface of the glass covered with a strong dew, which had evidently exhaled from the leaf. I again brought the leaf into contact with the glass, and, at the end of half an hour, found so much water discharged from the leaf, that it ran off the glass when held obliquely. I then inverted the position of the leaf, and placed its upper surface in contact with the glass: not the slightest portion of moisture now appeared, though the leaf was exposed to the full influence of the meridian sun. These experiments were repeated on many different leaves, and the result was in every instance precisely the same. It seems, therefore, that in the vine the perspiratory vessels are confined to the under surface of the leaf; and these, like the cutaneous lymphatics of the animal economy, are probably capable of absorbing moisture, when the plant is in a state to require it. The upper surface seems, from the position it always assumes, either formed to absorb light, or to operate by the influence of that body; and, if any thing exhale from it, it is probably vital air, or some other permanently elastic. fluid. It nevertheless appears evident in the experiments of Bonnet, that this surface of the leaves of many, when detached from the tree, readily absorbs moisture. Selecting two young shoots of the vine, growing perpendicularly against the back wall of my vinery, I bent them downwards, nearly in a perpendicular line, and introduced their succulent ends, as layers, into two pots, without wounding the stems, or depriving them of any portion of their leaves. In this position the shoots, which were about four feet long, and sprang out of the principal stem about three feet from the ground, grew freely, and in the course of the summer reached the top of the house. As soon as their wood became sufficiently solid to allow me to perform the operation with safety, I made two circular incisions through the bark of the depending part of each shoot, at a small distance from each other, near the surface of the mould in the pots; and and I wholly removed the bark between the incisions, thus cutting off all communication through the bark, between the layers and the parent stems. Had the subjects of this experiment now retained their natural position, much new wood and bark would have been formed at the upper lip of the wounds, and none at all at the lower, as I have ascertained by frequent experiments. The case was now different; much new bark and wood was ge. nerated on the lower lip of the wounds, become uppermost by the inverted position of the branches; and I have no doubt but that the new matter, thus deposited, owed its formation to a portion of sap, which descended by gravitation, from the leaves growing between the wounded parts and the principal stems. The result of this experiment appears to point out one of the causes why perpendicular shoots grow with much greater vigour than others: they have, probably, a more perfect and rapid circulation. The effects of motion on the circulation of the sap, and the consequent formation of wood, I was best able to ascertain by the following expedient-Early in the spring of 1801, I selected a number of young seedling apple-trees, whose stems were about an inch in diameter, and whose height between the roots and first branches, was between six and seven feet. These trees stood about eight feet from each other; and, of course, a free passage for the wind to act on each tree was afforded. By means of stakes and bandages of hay, not so tightly bound as to impede the progress of any fluid within the trees, I nearly deprived the roots and the lower parts of the stems of several trees of all motion, to the height of three feet from th ground, leaving the upper parts of the stems and branches in their na tural state. In the succeeding sum mer much new wood accumulated in the parts which were kept in me tion by the wind, but the lower parts of the stems and roots it creased very little in size. Rem 1. ing the bandages from one of the trees in the following winter. Its¢ a stake in the ground, about feet distant from the tree, on th cast side of it, and I attached the tree to the stake, at the height of six feet, by means of a slender pole, about twelve feet long; the leaving the tree at liberty to mov. towards the north and south, or more properly, in the segment of a circle, of which the pole formed i radius, but in no other direction. Thus circumstanced, the diameter of the tree from north to south, i that part of its stem which was most exercised by the wind, ex ceeded that in the opposite diret tion, in the following autumn, in the proportion of thirteen to eleven. These results appear to open an extensive and interesting field to our observation, where we shall find much to admire, in the means which nature employs to adapt the form of its vegetable productions to every situation in which art or accident may deposit them. If a tree be placed in a high and exposed situa tion, where it is much kept in motion by winds, the new matte: which it generates will be deposited chiefly in the roots and lower parts of the trunk; and the diameter of the latter will diminish rapidly a its ascent. The progress of the a cending sap will of course be in peded, and it will thence cause 13. teral |