Physiology

(ovucis, nature, and Acyog, - doctrine, science, or treatise.).The science of na. ture; physics; natural philosophy; the philosophy of physics or of nature. ao is the literal meaning of the word, and such was, at one time, the subject it was employed to designate. As the terms natural history, however, have been of late years limited-to the history of organized nature, physiology has, in like manner, been limited to the philosophy of natural history, in the same restricted sense; and is now commonly used to import general or synthetical views of organized life, whether in regard to plants or animals; and is occasionally, indeed, confined to those of animals alone. To controvert the erroneous use of a term is the purport of the etymologist, the grammarian, and the critic, but not of the editor of a dictionary of arts and sciences. We are therefore compelled to take the word in the common, though erroneous, sense in which we find it in the present day, and shall consider it as simply referring to the more important phenomena of vegetable and animal life. Vegetable Physiology. The best writers in the present day upon this subject as a whole are M. Wildenow, M. Mirbell, and Dr. Smith: besides whom, there are many others chat have touched upon particular parts with great advantage, and among these it would be unjust not to mention the names of Dr. Darwin, Mr. Knight, and Mr. Ellis.» We must, in as few words as we Can, give the general result of their separate pursuits and observations. Plants and animals are equally the progeny of seeds: there are other modes of production to be met with perhaps in both instances, as these of buds and bulbs, of slips and cuttings, but the common mode belonging to both is that of semination. The seed is sometimes naked, but more generally covered with a pericarp, whence plants become naturally divided into the two grand cla es of gymnospermous, and angiospermous. The pericarp is of various forms and structures; and of these the more common are the legume, silique, or silicle, being merely varieties of what, among ouselves, is denominated in popular language, cod or pod; the loment, which is a kind of pod not so frequent as either of the former, but of which we have an instance in the mimosas and ca ia fistula, the pome or core-apple, of which we have instances in the common-apple, and the orange; the drupe, or stone-apple, instances of which occur to us in the plum, cherry, and almond; the glume or chaff; the berry; the acinus or conglomerate berry, as in the rasp; the nut; and the capsule, Stripping off this outer covering, we find the seed to consist internally of a corculum, corcle, or little heart, and externally of a parenchymatous substance surrounded with a double intezument, sometimes single, sometimes bifid, and sometimes more than bifid, and hence denominated monocotyledonous, dicotyledonous, poly cotyledonous; in plain English, seed-lobes, or seed-leaves, single, double, or more than double. It was very generally supposed formerly, and is still supposed by some botanists, that the seeds of various orders of plants, as the mo es, fungi, and alge, are acotyledonous, or totally destitute of a cotyledon of any kind. But as many, perhaps most plants of this kind have of late been discovered to po e some such parenchyma, we have great reason to believe that this organ is universal, and that there is no such thing as am acotyledonous seed in the whole vegetable kingdom. In reality the cotyledon ap. pears absolutely nece ary for the germination and future growth of the seed, and may hence be denominated its lungs or placentule. Like the pers fect plant, it po e es lymphatics and air-ve els. Through the former of these it absorbs the moisture of the soil into which it is plunged, decomposes a part of it into its elementary principles, and conducts those principles together with the undecomposed water to the corcle, which becomes stimulated to the proce of germination by the oxygen thus set at liberty; while through the latter it breathes forth its exce of oxygen, together with a considerable portion of carbonic acid, and hydrogen ga es, and generally some portion of azot. It is the corcle, then, which is the true punctum saliens of vegetable life, and to this the cotyledon is subservient. The corcle consists of two parts, an ascending and a descending; the former called its plumule, which gives birth the trunk and branches, the latter denominated its rostel, which gives birth to the root and radicles. The position of the corcle in the seed is always in the vicinity of the hilum or eye, which is a cicatrix or umbilicus, remaining after the separation of the fun is or umbilical cord from the pericarp to which the seed has hereby been attached. he first radicle or germinating branch of the rostel uniformly elongates, and pushes into the earth, before the plumule evinces any change: like the cotyledon, the radicles consist chiefly of lymphatics and air ve els, which serve to separate the water from the soil, in order that the oxygen may be separated from the water. Hence originates the root, unquestionably the most important part of the plant, and which, in some sense, may be regarded as the. plant. itself: for if every other part of the plant be destroyed, and the root remain uninjured, this organ will regerminate, and the whole plant be renewed; but if the root perish, the plant becomes lost irrecoverably. Yet there are various phenomena in vegetable life that manifest a smaller difference in the nature of the root and the trunk, than we should at first be induced to suppose; for in several species, and especially those of the prunus and salix tribes, if the stem branches be bent down to the earth, plunged into it, and continued in this situation for a few mouths, these branches will throw forth radicles; and if, after this, the original root be dug up, and. suffered to ascend into the air, so that the whole plant become completely inverted, the original root will throw forth stem-branches, and bear the wild fruit peculiar to its tribe. The rhizophora, mangle or mangrove-tree, grows naturally in this manner; for its stem-branches, having reached a certain perpendicular height, bend downwards of their own accord, and throw forth root-branches into the soil, from which new trunks arise, so that it is not uncommon, in some parts of Asia and Africa, to meet with a single tree of this species covering the oozy waters in which it grows, with a forest of half a mile in length. The solid parts of the trunk of the plant consist of cortex, cuticle, or outer bark, liber, cutis, or inner bark, alburnum, or soft wood, lignum, or hard wood, and medulla, or pith. Linnéus gave ° the name of medulla to the pith of plants, upona supposition that it had a near resemblance to the medulla spinal is of quadrupeds. A closer invéstigation, however, has since proved, that this resem-= blance is very faint, and: that the pith er medulla: of vegetables consists of nothing more than a mere spongy cellular substance, forming indeed an admirable reservoir for moisture; and hence of the utmost importance to young plants, which, in consequence of their want of leaves and branches whose surfaces are covered with the bibulous mouths of innumerable lymphatics, would otherwise be frequently in danger of perishing through absolute drought; but gradually of le use as the plant advances in age, and becomes po est of these ern a mental appendages; and hence, except ina few instances, annually encroached upon, and at length totally obliterated by the surrounding lig~ num. All these lie in concentric circles, and the trunk enlarges, according to the theory of Grew ‘and Malpighi, by the formation of a new liber or inner bark every year; the whole of the liber of one. year, excepting indeed its outermost iayer, which is transformed into cortex, becoming the alburnum of the vext, and the alburnum becoming the lignum: but according to Mr. Knight’s recent and very ingenious and well supported theory, it enlarges by an annual transfer of a layer of the preceding year’s alburnum into a state of wood, a new layer being formed every year to take the place of that which is thus trausferred. Whence it is obvious, that a mark of any kind which has penetrated through the outer into the inner bark, must in a long proce of years be comparatively transferred to the central parts of the trunk; on which account we often find in felling trees of great longevity, as the oak, for example, the date of very remote national zras, and the initials of moe narchs who flourished in very early periods of our national history, stamped in the very heart of the timber on its being subdivided.