Botanists who wish to dry many plants without using much paper should place packets of 15 or 20 plants, arranged as we have just pointed out, in a stove with a current of air, heated up to 50 centigrades by a lamp placed below, and separated from the plants by a cross partition of punctured plate.
In twelve or twenty four hours the specimens are perfectly dry. This process, first successfully employed in Paris by M. Doyère, is most useful in warm and damp climates, and for plants difficult to dry; it is easily employed in scientific voyages.
Bamboo frames, found everywhere in tropical climates, replace excellently frames and bars of iron.
There is another more speedy process which requires much less paper, but preserves less perfectly the dried specimens. It only needs a dry and spacious room. The flowers are placed in a simple sheet of paper and pressed; then the sheets are spread out, for the night, on the floor, and, when dry, pressed again. This process it not so good as the former, and should be made use of only when there is a lack of paper.
This is all the art of making herbals; and every intelligent traveller knows how to suit his process to circumstances.
In damp times and regions, it is well to quicken the process of drying. Paper perfectly dry should only be used, and changed often. The paper should be dried in a warm oven, where bread has just been baked.
Watery plants, such as bulbs, orchides, etc., continue green in herbals several months after they are placed in them. It is well to plunge them in boiling water for one minute, or, still better, to put them in alcohol for a couple of hours; then they should be taken out and placed between two leaves of brown paper, where it dries easily, as the action of boiling water or alcohol has destroyed the life of the plant.
There are plants whose leaves or flowers easily break after drying; in such cases, all the parts should be sent separately.
There are families of plants that require peculiar processes of preservation. Palms, on account of their size, cannot be preserved in common herbals. Yet, it is important to complete the history of this remarquable family. For this, must be preserved:—1o The dried leaves in paper spread out, when they are not too large; folded like a fan, dried in the air and wrapped in brown paper well tied, when they are large.—2o Clusters of flowers or carymbs with the common envelope, taking care to preserve equally the male and female flowers, when they are separate; they should be dried quickly in the open air and wrapped in paper or cloth, taking care to collect the flowers that fall of. When these clusters are not large, it would be well to preserve them in weak alcohol, and, in all cases, it should be used for branches to be put in the same jar with ripe fruits of the same plant.—3o Clusters of ripe fruits dried in the air and other fruits in alcohol.
Those great marine plants, commonly known by the name of sea-weed, should be dried by hanging them in the shade, in the open air, without pressing them in paper; they should, afterwards, be put in paper bags, with a label of the place where they were collected and their color when fresh.