HERBARIUM, or Hortus Siccus, a collection of plants so dried and preserved as fully to illustrate their several specific characters. Sinee the same plant, owing to pecu-liarities of climate, soil, and situation, degree of exposure to light, and other influences, may vary greatly according to the locality in which it occurs, it is only by gathering together for comparison and study a large series of examples of each species illustrative of the flora of different regions that the laws of vegetable morphology, and many more points of scientific interest, can be satisfactorily determined. Thus, from the herbarium may be acquired a knowledge of those details concerning the minuter structure of individual plants which are of necessity omitted in works of systematic botany, as also of the relative taxonomic importance of the characters to be met with in large groups of forms.
Commencing with British herbaria, the collection of the Royal Herbarium at Kew, generally acknowledged to be at jonce the most extensive and the best preserved and most orderly in the world, comprises some 100,000 species, many of them represented by numerous specimens. It is arranged, for easy reference, in cases situate between the windows of the building containing it, the atmosphere of which is kept dry by means of hot-water pipes. In the intervening spaces are tables for the purpose of study, which is further facilitated by the presence in the same building of a large and valuable botanical library. Next in importance is the herbarium of the British Museum, which comprises assemblages of specimens gathered by numerous eminent botanists. The collection of Dillenius is deposited at Oxford, and that of the late Professor Harvey at Trinity College, Dublin. The original herbarium of Linnaeus is in the possession of the Linnean Society of London. With the more important British herbaria are to be ranked also those of Cambridge and Edinburgh. The collections of Jussieu and St Hilaire are included in the large herbarium of the Jardin des Plantes at Paris, and in the same city is the extensive private collection of Dr Cosson. At Geneva are three large collections,De Candolles, containing the typical specimens of the Pro-dromus, Delesserts fine series, and Boissiers Mediterranean and Oriental plants. The university of Götingen has had bequeathed to it the largest collection (exceeding 40,000 specimens) ever made b a single individualthat of the late Professor Grisebach. At the herbarium in Brussels are the specimens obtained by the traveller Martins, the majority of which formed the groundwork of his Flora Brasiliensis. Other national herbaria sufficiently extensive to subserve the requirements of the systematic botanist exist at Berlin, St Petersburg, Vienna, Leyden, Stockholm, Upsala, Copenhagen, and Florence. Of those in the United States of America, the chief, formed by Asa Gray, is the property of Harvard university; others are to be seen at Yale and Columbia colleges slid at New York and Michigan universities. The herbarium at Melbourne, Australia, under Baron Müller, has attained large propor-tions ; and that of the Botanical Garden of Calcutta is noteworthy as the repository of numerous specimens de-scribed by writers on Indian botany.
Specimens of flowering plants and vascular cryptogams are, at Kew, generally mounted on sheets of stout smooth paper, of uniform quality, and in most cases 17 inches long by 11 inches broad; the palms and their allies, however, and some ferns, require a size of 22 by 14 inches. The tough but flexible coarse grey paper (German, Fliesspapier), upon which on the Continent specimens are commonly fixed by gummed strips of the same, is less hygroscopic than ordinary cartridge paper, but has the disadvantage of affording harbourage in the inequalities of its surface to a minute insect, Atropos pulsatoria, L., which commits great havoc in clamp specimens, and which, even if noticed, cannot be dislodged without difficulty. The majority of plant specimens are most suitably fastened on paper by a mixture of equal parts of gum tragacanth and gum arabic made into a thick paste with water. Rigid leathery leaves are affixed by means of glue, or, if they present too smooth a surface, by stitching at their edges. Where, as in private herbaria, the specimens are not liable to be handled with great frequency, a stitch here and there round the stem, tied at the back of the sheet, or slips of paper passed over the stem through two slits in the sheet and attached with gum to its back, or simply strips of gummed paper laid across the stem, may be resorted to. A new adhesive substance, a kind of fish glue, has lately come into use for this purpose, and is highly spoken of. To preserve from insects, the plants, after mounting, are brushed over with a liquid formed by the solution of _ lb each of corrosive sublimate and carbolic acid in 1 gallon of methylated spirits. They are then laid out to dry on shelves iriade of a network of stout galvanized iron wire. After this are written, usually in the right-hand corner of the sheet, or oil a label there affixed, the designation of each species, the date and place of gathering, and the name of the collector. Information as to economical or medicinal properties may either be added thereto, or mentioned on the back of the sheet. It is especially important to attach to the name of the plant the initials or abbreviated name of the author by whom it was first described ; e.g., the words Ulva lactuca alone, might signify either of two distinct plants, the one described by Linnaeus, the other by Agardh. When the generic name has beep altered, but the specific name has been retained, the name of the original describer of the plant is placed in brackets before the name of the later author. Thus the Enteromorpha Grevillei of Thuret, having been renamed, has become Ulva Grevillei (Thur.), Le Jolis. The value of specimens in private herbaria is greatly enhanced by briefly stating on the lower left-hand corner of the sheet the characters that distinguish it from the plants most nearly resembling it. Other particulars as to habit, local abundance, soil, and claim to be indigenous may be written on the back, of the sheet, or on a slip of writing paper attached to its edge. It is convenient to place in a small envelope gummed to an upper corner of the sheet any flowers, seeds, or leaves needed for dissection or microscopical examination, especially where from the fixation of the specimen it is impossible to examine the leaves for oil- receptacles, and where seed is apt to escape from ripe capsules and be lost. The addition of a careful dissection of a flower greatly increases the value of the specimen. To ensure that all shall lie evenly in the herbarium the plants should be made to occupy as far as possible alter-nately the right and left sides of their respective sheets. The species of each genus are then arranged either systematically or alphabetically in separate covers of stout, usually light brown paper, or, if the genus be large, in several covers with the name of the genus clearly indi-cated in the lower left-hand corner of each, and opposite it the names or reference numbers of the species. Unde-termined species are relegated to the end of the genus. Thus prepared, the specimens are placed on shelves or movable trays, at intervals of about 6 inches, in an air-tight cupboard, on the inner side of the door of which, as a special protection against insects, is suspended a muslin bag, containing a piece of camphor.
The systematic arrangement varies in different herbaria. The works usually followed arefor dicotyledons, De Candolles Prodromus, and Endlichers or Bentham and Hookers Genera Plantarum; for monocotyledons, Kunths Enumeratio ; for ferns, Hooker and Bakers Synopsis Filicum; for mosses, Müllers Synopsis Huscorunt Frondo-sorum; for algae, Kützings Phycologia generalis; for hepaticae, Gottschie, Lindenberg, and Nees ab Esenbecks Synopsis Hepaticarum; and for other groups of cryptogamic plants the treatises of various authors scattered through numerous scientific publications. In certain herbaria, as in those of Boissier and Delessert at Geneva, the authority of the Prodromus is accepted only in the absence of any more recent treatise, or of a complete mono.graph on a. family. For the members of large genera, e.g., Piper and Ficus, since the number of cosmopolitan or very widely distributed species is comparatively few, a geographical c rouping is found specially convenient by those who are constantly receiving parcels of plants from known foreign sources. The ordinary systematic arrangement possesses the great advantage, in the case of large genera, of readily indicating, the affinities of any particular specimen with he forms most nearly allied to it in type. In the United States the species in the genera, and the genera in the orders, are usually arranged alphabetically, and the orders serially; sometimes, however, the genera are placed alpha-betically throughout without reference to the orders. The alphabetical arrangement, provided works on systematic botany are referred to for the identification of particular plants, possesses the advantage of permitting ready reference to any given species, and also of being independent of changes of classification ; but in Europe it is rarely adopted, on account of the counterbalancing practical in-conveniences it is considered to present. Instead of keep-ing a catalogue of the species contained in the herbarium, which, owing to the constant additions, would be almost impossible, such species are usually ticked off with a pencil in the systematic work which is followed in arranging them, so that by reference to this work it is possible to see at a glance whether the specimen sought is in the her-barium, and what species are still wanted. The custom commonly prevalent in Continental, especially German, herbaria of placing the dried specimens loosely between sheets of papers not always of uniform character is liable to lead to the admixture of nearly allied forms in intri-cate genera, such as Rubus, Rosa, Hieracium, Salix, &c., unless a label is attached to each specimen, a precaution not always adopted. In Germany Endlichers system is much followed for flowering plants, with the exception of palms, for which Martiuss arrangement is preferred. At Geneva De Candolles original herbarium is arranged in exact accordance with his Prodromus. In the other large herbaria in that city, the mounting and arrangement of the specimens are conducted much as in England, with the exception that smaller-sized sheets of paper are used for cryptogams.
Specimens intended for the herbarium should be collected when po,sible in dry weather, care being taken to select plants or por-tions of plants in sufficient number and of a size adequate to illustrate all the characteristic features of the species. When the root-leaves and roots present any peculiarities, My should invari-ably be collected, but the roots should be dried separately in an oven at a moderate heat. Roots and fruits too bulky to be placed on the sheets of the herbarium may be conveniently arranged in glass-covered boxes contained in drawers. The best and most effective mode of drying specimens is learned only by experience, different species requiring special treatment according to their several peculiarities, The chief points to be attended to are to have a plentiful supply of botanical drying paper, so as to be able to use about six sheets for each specimen; to change the paper at intervals of six to twelve hours; to avoid contact of one leaf or flower with another; and to increase the pressure applied only in proportion to the dryness of the specimen. To preserve the colour of flowers pledgets of cotton wool, which prevent bruising, should be introduced between them, as also, if the stamens are thick and succulent, as in Digitalis, between these and the corolla. A flower dissected and gummed on the sheets will often retain the colour which it is impossible to preserve in a crowded inflorescence. Before placing in a screw-press, should that be used, a flat sheet of Jead or some other suitable weight should be laid upon the top of the pile of specimens, so as to keep up a continuous pressure. Succulent specimens, as many of the Orchidaceoe, and sedunis and various other Crassulaceous plants, require to be killed by immer-sion. in boiling water before being placed in drying paper, or, instead of becoming dry, they will grow between the sheets. When, as with some plants like Verbascum, the thick hard stems are liable to cause the leaves to wrinkle in drying by removing the pressure from them, small pieces of bibulous paper or cotton wool may be placed upon the leaves near their point of attachment to the stem. When a number of specimens have to be submitted to pressure, ventilation is secured by means of frames corresponding in size to the drying paper, and composed of strips of wood or wires laid across each other so as to form a kind of network. Another mode of drying is to keep the specimens in a box of dry sand in a warm place for ten or twelve hours, and then. press them in drying paper. A third method consists in placing the speci-men within bibulous paper, and enclosing the whole between two plates of coarsely perforated zinc supported in a wooden frame. The zinc plates are then drawn close together by means of straps, and suspended before a fire until the drying is effected. By the last two methods the colour of the flowers may be well preserved, When the leaves are finely divided, as in Conium, much trouble will be experienced in lifting a half-dried specimen from one paper to another; but the plant may be placed in a sheet of thin blotting paper, and the sheet containing the plant, instead of the plant itself, can then be moved. Thin straw-coloured paper, such as is used for biscuit bags, may be conveniently employed by travellers unable to carry a quantity of bibulous paper. It offers the advan-tage of fitting closely to thick-stemmed specimens, and of rapidly drying. A light but strong portfolio, to which pressure by means of straps can be applied, and a few quires of this paper, if the paper be changed night and morning, will be usually sufficient to dry all except very succulent plants. When a specimen is too large for one sheet, and it is necessary, in order to show its habit, &c., to dry the whole of it, it may be divided into two or three portions, and each placed on a separate sheet for drying. Specimens may be judged to be dry when they no longer cause a cold sensation when applied to the cheek, or assume a rigidity not evident in the earlier stages of preparation.
Each class of flowerless or cryptogamic plants requires special treatment for the herbarium.
Marine algae are usually mounted on tough smooth white cart-ridge paper in the following manner. Growing specimens of good colour and in fruit are if possible selected, and cleansed as much as practicable from adhering foreign particles, either in the sea or a rocky pool. Some species rapidly change colour, and cause the decay of any others with which they come in contact. This is especially the case with the Ectocarpi, Desmarestice, and a few others, which should therefore be brought home in a separate vessel. In mounting, the specimen is floated out in a flat white dish containing sea-water, so that foreign matter may be detected, and a piece of paper of suitable size is placed under it, supported either by the fingers of the left hand or by a palette. It is then pruned, in order clearly to show the mode of branching, and is spread out as naturally as possible with the right hand. For this purpose a bone kuitting-needle answers well for the coarse species, and a camels-hair pencil for the more delicate ones. The paper with the specimen is then carefully removed from the water by sliding it over the edge of the dish so as to drain it as much as possible. If during this process part of the fronds run together, the beauty of the specimen may be restored by dipping the edge into water, so as to float out the part and allow it to subside naturally on the paper. The paper, with the specimen upwards, is then laid on bibulous paper for a few minutes to absorb as inuch as possible of the superfluous moisture. When freed from excess of water it is laid on a sheet of thick white blotting-paper, and a piece of smooth washed calico is placed upon it (unwashed calico, on account of its "facing," adheres to the sea-weed). Another sheet of blotting-paper is then laid over it; and, a number of similar specimens being formed into a pile, the whole is submitted to pressure, the paper being changed every hour or two at first. The pressure is increased, and the papers are changed less frequently as the specimens become dry, which usually takes place in thirty-six hours. Some species, especially those of a thick or leathery texture, contract so much in drying that without strong pressure the edges of the paper become puckered, Other species of a gelatinous nature, like Nemaleon and Dudresnaia, may be allowed to dry on the paper, and need not be submitted to pressure until they no longer present a gelatinous appearance. Large coarse algae, such, for instance, as the Fucaceoe and Laminarioe, do not readily adhere to paper, and require soaking for some time in fresh water before being pressed. The less robust species, such as Sphacelaria scoparia, which do not adhere well to paper, may be made to do so by brushing them over either with milk carefully skimmed, or with a liquid formed by placing isinglass (11 oz.) and water (112- oz.) in a wide-mouthed bottle, and the bottle in a small glue-pot or saucepan containing cold water, heating until solution is effected, and then adding 1 oz. of rectified spirits of wine; the whole is next stirred together, and when cold is kept in a stoppered bottle. For use, the mixture is warmed to render it fluid, and applied by means of a camels-hair brush to the under side of the specimen, which is then laid neatly on paper. For the more delicate species, such as the Callithamnia and Ectocarpi, it is an excellent plan to place a small fruiting fragment, carefully.floated out in water, on a slip of mica of the size of an ordinary microscopical slide, and allow it to dry. The plant can then be at any time examined under the microscope without injuring the mounted specimen. Many of the fresh-water algae which form a mere crust, such as Palmella cruenta, may be placed in a vessel of water, where after a time they float like a scum, the earthy matter settling down to the bottom, and may then be mounted by slipping a piece of mica under thein and allowing it to dry. Oscillatorioe maybe mounted by laying a portion on a silver coin placed on a piece of paper in a plater, and pouring in water until the edge of the coin is just covered. The alga by its own peculiar movement will soon form a radiating circle, perfectly free from dirt, around the coin, which may then be removed.
There is considerable difficulty in removing mounted specimens of algae from paper, and therefore a small portion preserved on mica should accompany each specimen, enclosed for safety in a small envelope fastened at one corner of the sheet of paper. Filamentous diatoms may be mounted like ordinary seaweeds, and, as welt as all parasitic algae, should whenever possible be allowed to remain attached to a portion of the alga on which they grow, some species being almost always found parasitical on particular plants. Ordi-nary diatoms and desmids may be mounted on mica, as above described, by putting a portion in a vessel of water and exposing it to sunlight, when they rise to the surface, and may be thus removed comparatively free from dirt or impurity. Owing to their want.of adhe.siveness, they are, however, usually mounted on glass as microscopic slides, either in glycerin jelly, Canada balsam , or some other suitable medium.
Lichens are generally mounted on sheets of paper of the ordinary size, several specimens from different localities being laid upon one sheet, each specimen having been first placed on a small square of paper which is gummed on the sheet, and which has the locality, date, name of collector, &c., written upon it. This mode has some disadvantages attending it: such sheets are difficult to handle; the crustaceous species are liable to have their surfaces rubbed; the foliaceous species become so compressed as to lose their characteristic appearance; and the spaces between the sheets caused by the thickness of the specimen permit the entrance of dust. A plan which has been found to answer well is to arrange them in cardboard boxes, either with glass tops or in sliding covers, in drawers-the name being placed outside each box, and the speci-mens gummed into the boxes. Lichens for the herbarium should, whenever possible, be sought for on a slaty or laminated rock, so as to procure them on flat thin pieces of the same, suitable for mounting. Specimens on the bark of trees require pressure until the bark is dry, lest they become curled; and those growing on sand or friable soil, such as Coniocybe furfuracea, should be laid carefully on a layer of guru in the box in which they are intended to be kept. Many lichens, such as the Verrucarioe and Collemaceoe, are found in the best condition during the winter months. In mounting collemas it is advisable to let the specimen become dry and hard, and then to separate a portion from adherent mosses, earth, &c., and mount it separately so as to show the branching of the thallus. Pertusarioe should be represented by both fruiting and sorediate specimens.
The larger species of fungi, such as the Agaricini and Polyporei, &c., are prepared for the herbarium by cutting a slice out of the centre of the plant so as to show the outline of the pileus, the attachment of the gills, and the character of the interior of the stem. The remaining two halves of the pileus are then lightly pressed, as well as the central slices, between bibulous paper until dry, and the whole is then "poisoned" and gummed on a sheet of paper in such a manner as to show the under surface of the one and the upper surface of the other half of the pileus on the same sheet. As it is impossible to preserve the natural colours of fungi, the specimens should, whenever possible, be accompanied by a coloured drawing of the plant. Microscopic fungi are usually preserved in envelopes, or simply attached to sheets of paper, or mounted as microscopic slides. Those fungi which are of a dusty nature, like the Myxomycetes, may, like the lichens, be preserved in small boxes, and arranged in drawers. Fungi under any circumstances form the least satisfactory portion of an herbarium.
Mosses when rowing in tufts should be gathered just before the capsules have become brown, divided into small flat portions, and pressed lightly in drying paper. During this process the capsules ripen, and are thus obtained in a perfect state. They are then preserved in envelopes attached to a sheet of paper of the ordinary size, a single perfect specimen being washed, and spread out near the envelope so as to show the habit of the plant. For attaching it to the paper a strong mucilage of gum tragacanth, containing, an eighth of its weight of spirit of wine, answers best. If not preserved in an envelope the calyptra and operculum are very apt to fall off and become lost. Scale-mosses are mounted in the same way, or may be floated out in water like sea-weeds, and dried in white blotting paper under strong pressure before gumming on paper, but are best mounted as microscopic slides, care being taken to show the stipules. The specimens should be collected when the capsules are just appearing above or in the colesule or calyx ; if kept in a damp saucer they soon arrive at maturity, and can then be mounted in better condition, the fruit-stalks being too fragile to bear car-riage in a botanical tin case without injury.
Of the Characeoe many are so exceedingly brittle that it is best to float them out like sea-weeds, except the prickly species, which may be carefully laid out on bibulous paper, and when dry fastened on sheets of white paper by means of gummed strips. Care should be taken in collecting charae to secure, in the case of dioecious species . ns of both forms, and also to get when possible the roots of those species on which the small granular starchy bodies or gemmae are found, as in C. fragifera. Portions of tile fructification may be preserved in small envelopes attached to the sheets.
See Bentham, Proc. Linn. Soc. Lond, 1869-70, p. xlvi. ; Johann Nave, Handy Book to the Collection and Preparation of Freshwater and Marine Algae., Lond. ; G. Rainann, Das Herbarium, Berlin, and Lasègues Musée botanique de JV. Benjamin Delessert, Paris, 1845. (E. M. H.)