that where lightning falls so powerfully as to calcine turf, some effect will be perceptible on the substrata of soil, or gravel, &c. for even quartz has been vitrified by lightning; but that no similar effect in any degree is to be discovered under fairy-rings, either recent or old, has been ascertained by accurate examination.

Instead of troubling you with any further observations of my own, in refutation of the above theory, permit me to close with a quotation from the accurate botanical work of the late Dr. Withering; in which, after describing the agaricus orcades, the author explains the phenomenon of fairy-rings in a more satisfactory manner than has been done by any other writer.

"I am satisfied that the rare and brown, or highly-clothed and verdant circles, in pasture-fields, called fairy-rings, are caused by the growth of this agaric. We have many of them in Edgbaston Park, on the side of a field sloping to the south-west, of various sizes; but the largest, which is eighteen feet in diameter, and about as many inches broad in the periphery, where the agarics grow, has existed for some years on the slope of an adjoining pasture-field, facing the south. The soil is there on a gravelly bottom. The larger circles are seldom complete. The large one just now described, is more than semi-circle, but this phenomenon is not strictly limited to a circular figure. Where the ring is brown and almost bare, upon digging up the soil, to the depth of about two inches, the spawn of the fungus will be found of a greyish white colour; but where the grass has again grown green and rank, I never found any of the spawn existing. A similar mode of growth takes place in some of the crustaceous lichens, particularly in the L. centrifugus, which spreads from a center to the circumference, and gradually decays in the middle; an observation made by Linnæus, and which is equally applicable to the general tendency of growth in the agaricus orcades.”

[Monthly Mag. vol. xv. Editor.

CHAP. IX.

PREPARATION AND USE OF AN HERBARIUM, OR HORTUS

SICCUS.

THE advantages of preserving specimens of plants, as far as it can

be done, for examinations at all times and seasons, is abundantly obvious. Notwithstanding the multitude of books filled with descriptions and figures of plants, and however ample or perfect such may be, they can teach no more than their authors observed; but when we have the works of Nature before us, we can investigate them for ourselves, pursuing any train of enquiry to its utmost extent, nor are we liable to be misled by the errors or misconceptions of others. A good practical botanist must be educated among the wild scenes of nature; while a finished theoretical one requires the additional assistance of gardens and books, to which must be superadded the frequent use of a good herbarium. When plants are well dried, the original forms and positions of even their minutest parts, though not their colours, may at any time be restored by immersion in hot water. By this means, the productions of the most distant and various countries, such as no garden could possibly supply, are brought together at once under our eyes, at any season of the year. If these be assisted with drawings and descriptions, nothing less than an actual survey of the whole vegetable world, in a state of nature, could excel such a store of information.

Some persons recommend the preservation of specimens in weak spirits of wine, and this mode is by far the most eligible for such as are very juicy. But it totally destroys their colours, and often renders their parts less fit for examination than the above-mentioned mode. It is besides incommodious for frequent study, and a very expensive and bulky way of making an herbarium.

The greater part of plants dry with facility between the leaves

of books, or other paper, the smoother the better. If there be plenty of paper, they often dry best without shifting; but if the specimens are crowded, they must be taken out frequently, and the paper dried before they are replaced. The great point to be attended to is, that the process should meet with no check. Several vegetables are so tenacious of their vital principle, that they will grow between papers, the consequence of which is a destruction of their proper habit and colours. It is necessary to destroy the life of such, either by immersion in boiling water, or by the application of a hot iron, such as is used for linen, after which they are easily dried. I cannot however approve of the practice of applying such an iron, as some persons do, with great labour and perseverance, till the plants are quite dry, and all their parts incorporated into a smooth flat mass. This renders them unfit for subsequent examination, and destroys their natural habit, the most important thing to be preserved. Even in spreading plants between papers, we should refrain from that precise and artificial disposition of their branches, leaves, and other parts, which takes away from their natural aspect, except for the purpose of displaying the internal parts of some one or two of their flowers, for ready observation.

After all we can do, plants dry very variously. The blue colours of their flowers generally fade, nor are reds always permanent. Yellows are much more so, but very white flowers retain their natural aspect. The snowdrop and parnassia, if well dried, continue white. Some greens are much more permanent than others: for there are some natural families whose leaves, as well as flowers, turn almost black by drying; as melampyrum, bartsia, and their allies, several willows, and most of the orchidea. The heaths and firs in general cast off their leaves between papers, which appears to be an effort of the living principle, for it is prevented by immersion of the fresh specimen in boiling water. Nandina domestica, a Japanese shrub, introduced among us by Lady A. Hume, and Mr. Evans, of Stepney, is very remarkable in this respect. Every leaflet of its very compound leaves separates from its stalk in drying, and those stalks all fall to pieces at their joints.

Dried specimens are best preserved by being fastened, with weak carpenter's glue, to paper, so that they may be turned over without damage. Thick and heavy stalks require the additional support of

a few transverse slips of paper, to bind them more firmly down. A half sheet, of a convenient folio size, should be allotted to each species, and all the species of a genus may be placed in one or more whole sheets. On the latter the name of the genus should externally be written, while the name of every species, with its place of growth, time of gathering, the finder's name, or any other concise piece of information, may be inscribed on its appropriate paper. This is the plan of the Linnæan Herbarium, in which every species, which its original possessor had before him when he wrote his great work, the Species Plantarum, is numbered both in pencil and in ink, as well as named, the former kind of numbers having been temporary till the book to which they refer was printed; after which they were confirmed with a pen, and a copy of the book, now also in my hands, was marked in reference to them. Here therefore we do not depend on the opinion merely, even of Linnæus, for we have always before our eyes the very object which was under his inspection. We have similar indications of the plants described in his subsequent works, the herbarium being most defective in those of his second Mantissa, his least accurate publication. We often find remarks there, made from specimens acquired after the Species Plantarum was published. These the herbarium occasionally shows to be of a different species from the original one, and it thus enables us to correct such errors.

The specimens thus pasted, are conveniently kept in lockers, or on the shelves of a proper cabinet. Linnæus, in the Philosophia Botanica, exhibits a figure of one, divided into appropriate species for each class, which he supposed would hold his whole collection, But he lived to fill two more of equal size, and his herbarium has been perhaps doubled since his death, by the acquisitions of his son and of its present possessor.

One great and mortifying impediment to the perfect preservation of an herbarium arises from the attacks of insects, A little beetle, called ptinus fur, is, more especially, the pest of collectors; laying its eggs in the germens or receptacles of flowers, and others of the more solid parts, which are speedily devoured by the maggots when hatched, and by their devastations paper and plants are alike involved in ruin. The most bitter and acrid tribes, as Euphorbia, Gentiana, Prunus, the syngenesious class, and especially willows, are preferred by these vermin. The last-mentioned family can

scarcely be thoroughly dried, before it is devoured. Ferns are scarcely ever attacked, and grasses but seldom.-To remedy this inconvenience, I have found a solution of corrosive sublimate of mercury in rectified spirits of wine, about two drachms to a pint, with a little camphor, perfectly efficacious. It is easily applied with a camel-hair pencil when the specimens are perfectly dry, not before; and if they are not too tender, it is best done before they are pasted, as the spirit extracts a yellow dye from many plants, and stains the paper. A few drops of this solution should be mixed with the glue used for pasting. This application not only destroys, or keeps off all vermin, but it greatly revives the colours of most plants, giving the collection a most pleasing air of freshness and neatness. After several years' experience, I can find no inconvenience from it whatever; nor do I see that any dried plants can long be preserved without it.

The herbarium is best kept in a dry room without a constant fire. Linnæus had a stone building for his museum, remote from his dwelling-house, into which, I have been told, neither fire nor candle was ever admitted; yet nothing can be more free than his collection from the injuries of dampness, or other causes of decay.

[Smith's Introduction to Physiological and Systematical Botany.