Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/751

H E R B A R I U M 717 indicating the affinities of any particular specimen with the forms most nearly allied to it in type. lu 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 leid to the admixture of nearly allied forms in intri cate genera, such as It-iibus, Rosa, ffieracium, Salix, &c., unless a label is attached to each specimen, a precaution not always adopted. In Germany Endlicher s system is much followed for flowering plants, with the exception of palms, for which Martina s arrangement is preferred. At Geneva De Candolle s original herbarium is arranged in exact accordance with his Prodromiis. 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 tlie herbarium should be collected when possible 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, they 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 lead 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 Orchidacece, and sedums 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 Verlascum, 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. Speci mens 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, Dcsmarcstice, 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 lingers 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 knitting-needle answers well for the coarse species, and a camel s-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 much 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 tex ture, contract so much in drying that without strong pressure the edges of the paper become puckered. Other species of a gelatinous nature, like Ncmalcon 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 algre, such, for instance, as the Fucaccae and Laminarice, 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 rnilk carefully skimmed, or with a liquid formed by placing isinglass (} oz. ) and water (1^ 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 camel s-hair brush to the under side of the specimen, which is then laid neatly on paper. For the more delicate species, such as the Cullithamnia 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 algre which form a mere crust, such as Palmella crucnta, 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 them and allow ing it to dry. OsciUatorice- may be mounted by laying a portion on a silver coin placed on a piece of paper in a plate, 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.