With regard to the mode or state in which plants are preserved, desiccation, accompanied by pressing, is the most generally used.  Some persons, Sir J.E.  Smith observes, 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 by the process of drying.  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 colors.  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.  The practice of applying such an iron, as some persons do, with great labor and perseverance, till the plants are quite dry, and all their parts incorporated into a smooth flat mass is not approved of.  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 practice 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.  The most approved method of pressing is by a box or frame, with a bottom of cloth or leather, like a square sieve.  In this, coarse sand or small shot may be placed; in any quantity very little pressing is required in drying specimens; what is found necessary should be applied equally to every part of the bundle under the operation.

Hot-pressing, by means of steel net-work heated, and placed in alternate layers with the papers, in the manner of hot pressing paper, and the whole covered with the equalizing press, above described, would probably be an improvement, but we have not heard of its being tried.  At all events, pressing by screw presses, or weighty non-elastic bodies, must be avoided, as tending to bruise the stalks and other protuberant parts of plants.