Herbal (Herbarium), gene-rally speaking, signifies a book, containing a methodical arrangement of the classes, genera, species, and varieties of plants, -together with an account of their properties. It is also applied to a hortus siccus, or dry garden ; an appellation given to a collection of specimens of plants carefully dried and preserved.
Among the different methods adopted by botanists, for obtaining a hortus siccus, the following appear to be the most practicable :
1. Lay the plants fiat between papers; then place,th:m between two smooth plates of iron screwed together at the cornets : in this.state they are to be committed to a baker's oven for two hours. Alter being taken out, they must be rub-bed over with a mixture consisting of equal parts of brandy and aquafortis, then pasted down on p. with a solution of gum-tragacauth in water, after which they are to be laid in a book, where they will adhere, and retain their original freshness. - Although this process was suggested by Sir R. Southwell, in the 237th Number of the Philosophical Transactions of the Royal Society, yet the following method is more simple :
2. Flatten the plant, by passing a common smoothing iron over the papers between which it is placed , and dry it slowly in a sand-heat. For this purpose, the cold sand ought to be spread evenly, the smoothened plant laid gently on it, and sand sifted over so as to form a thick bed ; the fire is then to be kindled, and the whole process carefully watched, till the plant is gradually and perfectly dried — Thus, the colour of the tenderest herb may be preserved, and the most delicate flowers retain all their pristine beauty.
3. Another, and far more complete method, was suggested by the ingenious Mr. Whately ; and bears a slight resemblance to that last specified.' He directs those who intend to follow his plan, previously to procure - 1. A strong oak-box of the same size and shape as those employed for packing up tin plates: 2. A quantity of line sifted sand, sufficient to fill the box : 3. A considerable number of pieces of pliant paper, from one to four inches square ; and, 4. Some small flat leaden weights, and a few small, bound books.
He then directs the specimen of the plant intended for the herbal to be gathered, when dry and in full bloom, with all its parts as perfect as possible, and conveyed home in a tin box, well secluded from the air. The plant is first to be cleared from the soil as well as the decayed leaves, and then laid on the inside of one of the leaves of a sheet of common cap-paper. The tipper leaves and flowers are next to be covered, when expanded, by pieces of the prepared paper, and one or two of the leaden weights placed on them. The remainder of the plant is now to be treated in a similar manner
The weights ought next to be gently removed, and the other leaf of the sheet of paper folded over the opposite one, so as to contain the loose pieces of paper : and plants between them. A book or two is now to be applied to the outside of "the paper, till the intended number of plants is thus prepared ; when a box is to be filled with sand to the depth of an inch, one of the plants put in, and covered with sand suf-ficient to prevent the form of the plant from varying. The other plants may then be placed in succession, and likewise covered with a layer of sand, one inch thick between each ; after which the whole is to be gently pressed down in a greater or less degree, according to the tenderness or firmness of the plants.
The box is next to be carefully placed before a fire, one side being occasionally a little raised, as may be most convenient; the sides being alternately presented to the fire, two or three times in the day; or, the whole may be put into an oven gently heated. In the course of two or three days, the plants will be perfectly dry, when the sand Ought to be taken out, and put into another box: the plants should1 likewise be removed to a sheet of writing paper.
This method of preserving plants, Mr. Whately states to be preferable to every other, as both the flowers and leaves, if kept loosely within the, paper, in a dry room, without being exposed to the air, will retain their beauty for several years. It will, however, be necessary to inspect them once in the course of a year, for the purpose of destroying any small insects, that may accidentally breed among the plants.