Preparation and Drying.
Specimens for drying should be as complete and characteristic as the circumstances of the case will allow. In many cases it is desirable to show the root, whether tufted or creeping, bulbous, tuberous, & c. Where there is any great difference of form or division between the radical and cauline leaves specimens of each should be preserved. Usually it is desirable to have not only the flowers but the fruit; in some orders the fruits are indispensable, as in the sedges. When the specimens are larger than the herbarium-sheets they may be cut into suitable lengths, or if slender the stem may be partially broken across or simply folded. The stiff and wiry stems of grasses and sedges, & c., may be kept in place by passing the folded portion through a slit in a piece of stiff paper. When the root or stem is thick, or too large to press without inconvenience, it should be split down the middle, or one side should be pared down. All unisexual plants, as Coprosma, Podocarpus, Clematis, & c., should be represented by specimens of the staminate and pistillate flowers, and whenever possible the fruiting specimens should be taken from the same plant as the female flowers. Fleshy plants, as Mesembryanthemum, should be placed in boiling water for two or three minutes, but should be wiped perfectly dry before being placed in the press. Bulbs, corms, tubers, & c., may be advantageously treated in the same manner. All specimens should be slightly shorter than the herbarium-sheets.
The simplest method of drying plants is to place them between sheets of absorbent paper under sufficient pressure to prevent the specimens from shrivelling or becoming brittle. In order to insure the perfect abstraction of moisture the damp papers must be replaced by dry ones at frequent intervals, which, except in the case of grasses and other thin plants containing very little moisture, should never exceed twenty-four hours for the first four days after specimens are placed in the press, and it will be all the better if the first change can be made within twelve hours. It is of the greatest importance that the damp papers should be removed at least daily for the first four or six days, as neglect at this stage cannot be remedied afterwards: neglected specimens, especially of soft plants, become discoloured, and never lose the whole of their moisture, but assume a flaccid condition, which renders them more liable to the attacks of insects and Fungi than specimens
that have received proper attention. Aquatic plants should have the external moisture wiped off before being placed in drying-papers, and should receive their first change within three or four hours of their being placed in the press.
The drying-papers should be of the same dimensions as the herbarium-sheets; the best quality is “Bentall's Botanical Drying-paper,” which is manufactured specially for this purpose, and costs in London 19s. per ream for demy, 18in. by 11in. when folded. The well-known chalk-paper is almost equally good, but is more expensive; both these papers are of high absorbent-power and great durability. Thick blottingpaper is good, but not durable; old newspapers or any common paper may be used when better kinds cannot be obtained; the coarse brown paper tarred on one side for packing purposes affords good results. It need scarcely be said that, whatever kind of paper may be used, the sheets should be of uniform size, and when of thin quality several sheets should be folded together to save trouble in changing.
As already pointed out, if the specimens are placed on thin sheets at first, a great saving of time and labour will be obtained, especially with small or flaccid specimens, as the entire sheet can be placed between the drying-papers at once instead of lifting each specimen separately. Each specimen should be carefully laid out in such a way that the branches do not cross each other, and the flowers are properly displayed; some of the leaves should be arranged with the lower surface upwards. The specimen should be accompanied by a label showing the name of the plant, the locality in which it was grown, the date of collection, and the collector's name. Notes on habit, structure, & c., should be entered in the collector's note-book. On the specimen thus arranged two or more folded dryingpapers should be laid, according to the quantity of moisture it contains, and the process must be repeated until all the specimens are disposed of. Care must be taken to divide the pile of specimens into sections by boards the size of the drying-papers, and ⅜in. or ½in. in thickness: stout cardboard will answer the purpose very well. Boards of the kind-should also be used to separate plants gathered at different times. The pile of specimens must be placed under pressure, which may be applied in various ways. A board may be placed on the top, and the whole weighted with bricks, or bags of sand, or stones, & c; or cleated boards may be placed at the top and bottom of the pile, and the whole tightened with strong straps and buckles. A press of this kind forms a convenient travelling-press; thick sole-leather in place of the covering-boards increases its portability, but requires an additional strap which should be applied lengthwise. The most convenient form of press, however, is the screw-press. It is sometimes
urged against the screw-press that the pressure becomes relaxed as the moisture is extracted from the specimens. This, however, is theoretical rather than practical. As a matter of fact, when a press receives proper attention, and the wet sheets are replaced by dry ones—say, on alternate days—the pressure is not perceptibly relaxed: even if it were necessary to leave the press unchanged for several days, nothing would be more easy than to give an occasional turn of the screw.
A simple but effective portable screw-press which I have had in use for over forty years is made of ½in. square iron, forming a frame 11 ½in. wide by 12in. in height; the middle portion of the upper side is enlarged and perforated with a chased aperture to receive the screw, which is from 6in. to 7in. long (including the head), and terminates in an obtuse point below. The exact weight of a press 11 ½in. by 12in. is 51b.; a smaller size might be made out of ⅜in. square iron. A press of this kind never gets out of order, and is almost unbreakable, while it is quite as portable as a strap-press. Two of these portable presses may be carried on a pack-horse, leaving ample space between them for the tent and other field impedimenta. On Plate XXVIA. is shown the form of the press and the way in which it is used.
The amount of pressure required varies with the nature of the specimen. Many ferns and slender grasses, such as Poa trvialis and Microlcena stipoides, do not require more than from 20lb. to 30lb., but twice this weight would not be too much for robust kinds such as Arundo conspicua, Danthonia flavescens, & c. From 50lb. to 80lb. is sufficient for most herbaceous and for many woody plants, while from 80lb. to 100lb., or more, may be used for the larger species of Aciphylla and for stout, wooded plants with thick leaves. Overpressed specimens are often useless for examination.
With regard to the number of changes of paper and the length of time required for drying different plants, it is hardly possible to lay down hard-and-fast rules, as so much depends upon the state of the atmosphere. Slender grasses and ferns require but two or three changes, and may often be dried in a week or ten days; most plants, however, require at least a fortnight; thick-leaved and fleshy plants require three or four weeks, or longer. Submerged aquatic plants dry very quickly after the second or third change. But in these and similar matters a little practice and observation are of more value than much teaching.
Instead of solid boards for the top and bottom of the press, and for dividing it into sections, ventilators are sometimes employed. These may be made in various ways—say, of two interrupted layers of bars ½in. square of any common wood, the
length of each layer being regulated by the length or width of the drying-papers. The bars should be laid about 2in. or 2 ½in. apart, one layer crossing the other at a right angle, the whole being secured by wire nails at the points of intersection. A press arranged with ventilators on this plan does not require such frequent changes of paper, as much of the moisture is drawn off by air-currents passing through, the ventilators, the amount largely depending upon the state of the atmosphere. In wet weather ventilators are of but little value. Sometimes the ventilators are made of woven wire strengthened by a marginal iron frame, but, except for outside covers, the results are less satisfactory than with the wooden ones previously described. A press of this kind may be placed in an open Window with advantage.
The process of drying may be shortened by placing the press in a large oven, by using hot drying-papers, or by passing hot flat-irons over the separate layers of specimens.
The time requisite for preparing really good specimens, and the frequent changes of drying-papers required, have led to many attempts to discover some improved process, but the results have not been altogether satisfactory: still, two of these processes deserve brief mention.
Rather thick absorbent brown paper may be saturated with chloride of lime in solution. The sheets should then be dried in an oven, and enclosed in a perfectly air-tight box until wanted for use. The specimens should be laid in folded sheets of any thin paper, which should be placed between the prepared drying-papers, pressure being given by straps and buckles, when the press should be placed in an air-tight box, or protected from the atmosphere by being wrapped in oiled cloth. Ordinary specimens do not require more than a single change of drying-papers, and become thoroughly dry in a few days, the colour being well preserved; but, as a rule, specimens prepared in this way are very brittle. The dryingpapers can only be deprived of absorbed moisture by being placed in an oven, and care must be taken to keep them fit for use by preventing the access of air as completely as possible.
A more advantageous process is to saturate water with sulphurous acid; then to add methylated spirit in the proportion of one to three. Thick-leaved plants, such as the larger species of Celmisia, & c., should be soaked in the fluid from twelve to twenty-four hours, according to the succulence of the leaves and stem. Plants with still thicker leaves may require from one to two days; while delicate and thin-leaved plants should only remain in the liquid from five minutes to an hour. It is imperative that all external moisture be removed by wiping or by exposure to dry heat before the specimens are placed in the press. Thin-leaved plants
treated by this process require a single change of dryingpapers only; those with thick leaves rarely require more than three changes; so that time and labour are greatly reduced, while the colour of the flowers is better preserved than by any other process. It is, however, better adapted to herbaceous than to woody specimens. The methylated spirit might first be saturated with corrosive sublimate, when the specimens would be poisoned without further trouble.