VEGETABLE PHYSIOLOGY.

THE Society for the Promotion of Popular Instruction, under whose auspices this and some other volumes have been published, is a body that seems to rely more upon the works it issues than the names of its members for the acquisition of repute. Their publica- tions have hitherto been reprints or translations ; and though the choice has been good, the price reasonable, and the execution of what was done respectable, they have not possessed such a marked character as very clearly to discriminate them from individual speculations : but the volume, or rather the part before us, (for Vegetable Physiology is to be followed by Botany,) is an original undertaking, and of a superior kind. Fertile as is our time in endeavours to present the essential principles and striking facts of science in an attractive form, we have met with nothing equal to the Vegetable Physiology "published by the Society for the Pro- motion of Popular Instruction." It displays a fulness of knowledge with great powers of popularly conveying it, and a clear and me- thodical general arrangement, as well as a judicious selection of particular facts for the purpose of illustrating general principles. Igor is it mere abstract knowledge which is presented : at every proper opportunity physiology is applied, either to the object of private recreation—as in cultivating flowers—or to the higher pur- poses of agricultural improvement and foreign commerce. The sixth chapter, on "the Food of Plants and the manner in which it is obtained," should be read by every intelligent agriculturist in the country, whether he cares about the principles of vegetable physiology or not.

After a general introductory view of vegetation, the subject is handled in a dozen chapters, discussing the general characteristics of organic or living as distinct from inorganic substances, and the difference between animals and vegetables ; the elementary struc- tures or tissues of plants ; the structure and functions of their roots, stems, and leaves ; their nutritive, secretory, and reproductive powers ; together with some general remarks on the motions of plants, and the production of light, heat, and electricity by their means.

We have spoken of the Vegetable Physiology as a compilation, or at least an exposition of scientific knowledge, in which the manner is essentially the chief merit. Nor has the work any claims to original discovery, or to the presentation of a connected series of original observations, or of any observation beyond that which all intelligent persons are continually making in any pursuit which they follow. But the author has this original merit—he takes an enlarged and comprehensive view of his subject, and of the truths which it contains, so as to suggest to the reader many things connected with the phenomenon of life and the principles of phi- losophy,—the close connexion which all created objects bear to one another ; the remote dependence of the highest upon the lowest class of beings for the possibility of existence ; and the means, simple, gradual, but certain, by which Nature, through successive permu- tations of form, prepares even the barren rock to support the higher class of animantia. An example of the qualities we speak of will be found in this account of the

UNIVERSALITY OF VEGETABLE LIFE.

Wherever circumstances are compatible with vegetable existence, there we find plants arise. It is not only on the luxuriant soil, on which many genera- tions have flourished and decayed, that we find the display of their beauties. The coral island, but recently elevated above the level of the sea, speedily be- comes clothed with verdure. From the materials of the most sterile rock, and even from the yet recent cinders and lava of the volcano, nature prepares the way for vegetable existence. The slightest crevice or inequality is sufficient to arrest the invisible germs that are always floating in the air ; and the hum- ble plants which spring from these soon overspread the surface, deriving their chief nutriment from the atmosphere. Having completed their allotted period of existence, they die and decay ; but their death is only a preparation for the appearance of higher forms of vegetable structure. They are followed by suc- cessive tribes of plants of gradually increasing size and strength ; until, in the course ofyears, the sterile rock is converted into a natural and luxuriant garden, of which the productions, rising from grasses to shrubs and trees, pre- sent all the varieties of the fertile meadow, the tangled thicket, and the widely- ;Treading forest.

No extremes of heat or cold seem to put an entire check upon vegetation. Even in the desert plains of the torrid zone, the eye of the traveller is often re- freshed by the appearance of a few hardy plants, which 8n4 sufficient materials for their growth in these arid regions. And wherever a spring of water moistens the soil and atmosphere around, a spot of luxuriant verdure is found. • • •

Many remarkable facts might be mentioned relative to the degree of heat which some forms of vegetation are capable of sustaining, and which, to some species indeed, appears a natural and even necessary condition. A hot spring in the Manilla Islands, which raises the thermometer to 187 deg., has plants flourishing in it and on its borders. In hot springs near a river of Louisiana, of the temperature of from 122 deg. to 145 deg., have been seen growing not merely the lower and simpler plants, but shrubs and trees. In one of the Geysers of Iceland, which was -hot enough to boil an egg in four minutes, a species of Chara bas been found growing and reproducing itself; and vegeta- tion of an humble kind has been observed in the similar boiling-springs of Arabia and the Cape of Good Hope. One of the most remarkable facts on re- cord, in reference to the power of vegetation to proceed under a high tempera- ture, is related by Sir G. Staunton, in his account of Lord Macartney's Em- bassy to China At the island of Amsterdam a spring was found, the mud of which, far hotter than boiling water, gave birth to a species of liverwort. A large squill bulb, which it was wished to dry and preserve, has been known to push up its stalk and leaves, when buried in sand kept up to a temperature much exceeding that of boiling water.

Even the extreme of cold is not fatal to every form of vegetable life. In the realms of perpetual frost, the snow which covers mountains and willies, and whose surface scarcely yields to the influence of the solar rays at midsummer, is in some places reddened for miles together by a minute vegetable, which rows in its substance, and has been supposed, from its very rapid increase, to have fallen from the sky. This will be hereafter described under the name of red snow which is that commonly applied to it. The lichen which forms the winter food of the reindeer, grows entirely buried beneath the snow ; and its quantity may be judged of by the number of the animals which find in it their sole support during a considerable part of the year.

Plants are found, too, in situations in which some peculiar noxious influence might be supposed entirely to prevent their growth ; as, for example, in sul- phureous springs. In fact, there are scarcely any circumstances in which there is not some kind of plant adapted to exist. Thus, it is well known that soils which have any considerable admixture of metallic ores are not favourable to most kinds of vegetation ; and among such, those mixed with the refuse of lead-mines are the most sterile ; so that this substance is often mixed with gravel, to prevent weeds from growing on garden-walks. Yet even on heaps. of this material, thrown up around the openings of the mines, the vernal sand- wort thrives, growing perhaps even more luxuriantly than in any other situation.

Of plants many are rare ; that is, adapted to such peculiar cir- cumstances of soil, temperature, atmosphere, and so forth, as to be only found where the necessary combinations are perfectly obtained. Others are common ; having a power of adaptability which enables them to flourish almost anywhere—as the potato, grain, or leguminous plants ; and even apparently to change their character with the changing nature of soil and cultivation—as the cabbage, broccoli, cauliflower, all varieties of one species. In less important vegetables, and in another way, this power of adaptation may be seen by the student of nature both on a large and a small scale.

" This adaptation of each species to particular circumstances is often seen in an interestin* manner on a small scale, on the exterior of large trunks of trees, old towers, ec. which are thickly clothed with mosses and lichens. Many of these avoid the light ; and their presence indicates the north side of the body to which they are attached. To others, again, the light in all its strength is ge- nial ; and they frequent the southern aspect ; whilst other forme, intermediate in habits, frequent the eastern and western sides; so that on going round such a tower or large trunk, we observe a succession of different species, which may be compared to that which is presented in the various latitudes, passing from the equator towards the pole. A similar succession on a larger scale is seen on ascending a high mountain between the Tropics, such as the Peak of Teneriffe. The lower portion exhibits the vegetation of the surrounding country, in all the luxuriance and richness of an island in the torrid zone. Higher up, the traveller meets with productions similar to those found on the borders of tem- perate regions; and to these succeed those of the medium temperate zone. Above these are perceived the alpine plants, which in Northern Europe are found at a comparatively trifling elevation ; and to these succeeds the dreari- ness of perpetual snow. These five distinct zones are well marked on the Peak of Teneriffe; each having a certain set of plants peculiar to it, as the plants of Northern and Southern Europe and of Northern and Central Africa are to those regions respectively."

CHARACTERISTICS OF MOSSES.

Mosses are found in all parts of the world in which the atmosphere is moist; but they are far more abundant in temperate climates than in any between the Tropics. They are among the first vegetables that clothe the soil with verdure in newly-formed countries ; and they are the last that disappear when the atmosphere ceases to be capable of nourishing vegetation. The first green crust upon the cinders with which the surface of Ascension Island was covered, consisted of minute mosses. This tribe forms more than a fourth of the whole vegetation of Melville Island, one of the most Northerly spots in which any plants have been observed; and the black and lifeless soil of New South Shet- land, one of the islands nearest to the South Pole, is covered with specks of mosses struggling for existence.

Besides their power of resisting extremes of temperature, mosses exhibit a remarkable tenacity of life, when their growth is checked by the absence of moisture; so that they may often be restored to active life even when they have been dried for many years. Hence they offer abundant sources of interest to the observer of nature at a season when vegetation of other kinds is almost entirely choked. For it is most curious to observe how gay these little mosses are on every wall-top during the winter months and in the early spring,— almost or perhaps the only things which seem to enjoy the clouds and storms of the season. They choose the most exposed situations, spread out their leaves and push up their delicate urns amidst rain, frost, and snow ; and yet there is nothing in their simple and tender structure from which we could infer their capability of resisting influences so generally destructive to vegetation.

OPERATION OF LICHENS.

To the lichens may well be applied the title of Vernactili, or bond-slaves; which Linnwus fancifully gave to the sea-weeds, regarding them as fettered to the rocks on which they grow. For the lichens seem as it were chained to the soil which they labour to improve for the benefit of others, although they derive no nourishment from it themselves. The mode in which they prepare the sterile rock for the reception of plants which require a higher kind of nourishment, is most remarkable. They may be said to dig for themselves graves for the reception of their remains, when death and decay would other- wise speedily dissipate them : for whilst living, these lichens form a consi- derable quantity of oxalic acid, (which is a peculiar compound of carbon and oxygen, two ingredients supplied by the atmosphere,) and this acts chemically upon the rock, (especially if of limestone,) forming a hollow which retains the particles of the structure when their term of connected existence has expired. The moisture which is caught in these hollows finds its way into the cracks and crevices of the rocks ; and when frozen, rends them by its expansion into minute fragments, and thus adds more and more to the forming soil. Suc- cessive generations of these bond-slaves continuously and indefatigably perform their duties ; until at length, as the result of their accumulated toil, the barren and insulated reeks, or the pumice or lava of the volcano, become converted into fruitful fields. For when Flora's standard has once been planted on tracts thus claimed, they are soon colonized by plants of other tribes. The mosses, ferns, and other cryptogamia follow them ; and at last, by the growth and decay of successive generations of plants, a sufficient thickness of soil is produced for the nourishment of the luxuriant herbage and the support of the lofty forest- tree. And thus, by the labours of these apparently insignificant plants, men are enabled to reap their harvest and to supply themselves with timber from the forests, and cattle increase and multiply on what was formerly but snaked and desolate rock.

DIFFUSION OF FUNGI SEED: A HINT TO HOUSEWIVES.

The number of these germs is almost incalculable. Thus, the fine dust which issues from the common puff-ball when mature, consists entirely of these little bodies, which are diffused through the air, and seem to float about in it, ready to develop themselves when they meet with the fitting conditions. In a single fungus above ten millions have been counted ; and these were probably by no means the whole number contained in it. When these minute germs are once spread through the air, there are so many means provided for their diffusion' that it is difficult to conceive of a place from which they should be excluded.

However improbable, then, it may at first sight appear, that every portion of the air we breathe should contain the germs of a large number of species of fungi, ready to develop themselves whenever the peculiar conditions adapted to each kind are presented, there seems good reason to believe that such is the case ; and in this manner we may account for several facts of some practical importance relative to the production of those very troublesome forms of vege- tation known by the names of mould, mildew, flee. It is well known that fruit-preserves are very liable to be attacked by the common bead-mould; which no care employed in completely closing the mouths of the jars can pre- vent. It has been remarked, however, that they are much less liable to suffer in this way, if not left open for a night before they are tied down ; and it is therefore probable that the germs of the mould sow themselves, as it were, in this luxunant soil, before the jar is covered. Again, there is a particular kind of cheese, much valued by some epicures, which !derives its peculiar flavour from the quantity of fungous vegetation it contains. It is prepared simply by breaking up the curd and exposing it for a day or two, in small lumps laid upon a cloth, to the sun and air ; it there seems to receive the germs of fungi, which afterwards vegetate in it, and spread their growth through the mass whilst it is yet Sat.

HINTS TO HORTICULTURISTS AND AGRICULTURISTS.

These facts have an important influence on the operations of the cultivator, whether they be on the large scale of the farmer or the small one of the gar- dener. No manure is more serviceable in yielding carbonic acid than that which consists of decaying vegetable matter ; and this is more abundant than is commonly imagined. A small garden attached to a dwellinghouse may be *niched with an ample supply of rich manure by throwing into a pit all the refsme vegetable matter of the kitchen, and that supplied by the garden itself, in the form of weeds, dead leaves, prunings of fruit trees, &c.; these should be lightly covered with earth, and kept slightly moist, and frequently exposed to the air by being turned over with the spade. And in a farm there will seldom be any deficiency of similar materials, if none are wasted. Weeds, for example, should not be burned unless they are in seed ; for they may be made to afford a valuable supply of nutriment, instead of withdrawing it. A manure of this kind is to many plants more serviceable than that furnished by animals. Some remarkable examples are on record of the influence of it upon the growth of vines, which may be here advantageously introduced, as interesting illustrations el the foregoing principles.