Art. XXXVIII.—On the Preparation and Preservation of Botanical Specimens.
[Read before the Nelson Philosophical Society, 5th November, 1894.]
Although the process of drying plants for the herbarium is simple and inexpensive, it is no uncommon thing to find collections of specimens which are almost worthless for critical examination owing to the imperfect manner in which they have been prepared. In others the specimens are of little value owing to their fragmentary character. Culms of grasses without leaves, sedges destitute of fruits, the staminate flowers of a Coprosma without the pistillate, or the pistillate without the staminate, are of but little use to any one desirous of gaining a thorough knowledge of the plants under examination. Yet again, even well-selected and carefully-dried specimens, if without labels stating the locality in which each was gathered, are of no value to the student who desires to become acquainted with their geographical distribution. It may therefore be worth while to describe the simple apparatus required, and indicate the chief points which should receive attention in the preparation and preservation of herbarium specimens, although it is not easy to say anything now on a subject of this description.
For field-work the collector will require a strong digger or trowel, in order to obtain tubers, bulbs, & c., in an undamaged condition. The blade should be 6in. or 7in. in length, concave on the upper surface, 1 ½in. broad at the base, tapering to a narrow, rounded end, with sharp edges. The shank should be continued upwards for about 4in., and should have a piece of puriri or other hard wood riveted in the front and shaped to form a convenient handle. An old file may be made into an unbreakable digger by any intelligent blacksmith.
The vasculum, or collecting-box, may be of any convenient size or shape, according to the fancy of the bearer. It should be made of light sheet-zinc or tin, and lacquered both inside and out. Where a large number of specimens is not required, its length may be from 20in. to 24in. by 6in. or 7in. broad, and from 4in. to 5in. in depth. The sides and ends should be convex, and the lid should open nearly the full length and width of the upper side. A stout handle, large enough for the hand to be passed through, should be attached to the upper end, and two strong loops should be fixed on one side to allow of the box being carried by a strap when required.
Many collectors prefer to use a portfolio, which, like the vasculum, may be made of any convenient size; usually it will be found most advantageous if of the same dimensions as the herbarium-sheets. It can be made of two stout millboards covered with American cloth, and connected by a leather back. The whole should be secured by two light straps, with buckles, so that pressure may be regulated as required; and a convenient handle should be attached. It should be filled with folded sheets of any thin soft paper, about ¼in. shorter and narrower than the covers. Old newspapers cut to the proper size will answer the purpose. The specimens should be laid in the loose sheets, and the sheets removed to the drying-press on reaching home. It saves much time and trouble to keep small, delicate, or flaccid specimens in these rough papers until they are thoroughly dry.
For very small specimens a pocket press the size of an octavo volume is very serviceable. It may be made of common blotting-paper, with cardboard covers secured by stout twine, or even by elastic rings. A book may easily be utilized for a pocket press if nothing better can be obtained.
Thin sheet guttapercha will often be found a great convenience especially when collecting aquatic plants, in the absence of a portable press. Isoetes, Naias, Potamogeton, and other water-plants, it tightly wrapped in this material, and packed so as to prevent bruising, may be kept in good condition for a week of ten days, and carried hundreds of miles without injury.
Many plants may be kept in the vasculum for several days if needed without sustaining injury. During protracted excursions this is occasionally a great convenience, but as a rule specimens should be placed in the drying-press as soon as possible after they are collected.
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.
Algæ, Musci, Characeæ, etc.
Delicate aquatic plants such as the finer marine Algæ require special treatment. A portion of the plant should be removed and after careful washing floated in a bowl of fresh water, when a suitable white paper may be placed underneath and the specimen gently lifted out. A camel-hair pencil may be used to arrange small branchlets while floating, and superfluous portions should be cut away with fine-pointed scissors before the specimen receives the final touches. The floated specimen should be placed on thick blotting-paper, and a sheet of oiled paper laid between the specimen and the superincumbent drying-paper to prevent adhesion. The pressure required in drying these delicate plants is very small, but they should receive their first change within two hours of being placed in the press; if changed quickly and frequently they become dry in two or three days. The larger coarse Algæ should be washed in fresh water and pressed in the usual way, oiled paper being placed immediately above the gelatinous species.
Full instructions for the preparation of Fungi and unicellular Algæ are outside the scope of this paper, but may be found in any good work on the preparation of objects for the microscope.
The delicate species of Nitella may be treated in the same manner as marine Algæ. Most of the species of Chara are strongly calcareous, and should receive the same treatment as ordinary flowering-plants; they are, however, easily destroyed by excess of pressure.
Mosses are easily dried in the ordinary manner. They require but few changes and little pressure. The finer kinds of Hepaticæ are remarkably delicate, and must be treated carefully, as overpressed specimens are of no value. Thick red blotting-paper is the best material for drying these delicate plants. The coarser Hepaticæ and liverworts may be dried in the ordinary manner. The same process may be applied to foliaceous lichens, but rupestral and saxicolous kinds and many Fungi are best preserved by drying at an air-temperature of from 80° to 90° Fahr., and mounting on small cards with a fragment of the rock or bark on which they grow.
A heterogeneous collection of dried plants, however well preserved, is of very little service, and can scarcely be termed an herbarium. The specimens must be named and arranged in a systematic manner so as to admit of easy reference, in order to economize time and labour. The herbarium may comprise the plants of a small district only, as of the Port or Provincial District of Nelson, or it may comprise the plants of an entire continent. It should be kept in an air-tight and dust-proof cabinet.
The first point to be determined is the size of the herbarium-sheets. Attention has been drawn to the desirability of the drying-papers being of the same size as the herbarium-papers, but the dimensions have not been considered. Much will depend upon the taste of the collector, but practically the choice lies between foolscap, demy, and folio. The first—13in. by 8in.—although often used for private collections, is rather too small to allow of characteristic specimens of many New Zealand plants. The first cost of the third—20in. by 12in. or 14in.—is needlessly large, while it is very cumbrous in the field, and involves an unnecessary expenditure of time and labour, without securing any corresponding advantage. Sheets of demy size, 18in. by 10in. or 11in., afford the maximum amount of convenience. In some herbaria the sheets are equal in length and breadth. The Linnean Herbarium is mounted on sheets of foolscap size; Bentham's Herbarium on small demy, 16 ½in. by 11in.; Cunningham's New Zealand Herbarium, on folio.
The sheets should be non-absorbent, hard, firm, and of even texture. A pale-brown tint similar to that of light cartridge-paper is to be preferred to white. All papers used in the herbarium should have perfectly even margins; even labels should not be exempted from this rule, as ragged margins invite the attacks of certain insects.
For all public herbaria, at least, the specimens should be poisoned before mounting. In private collections mounting may be dispensed with, and the specimens simply laid on the sheets. If the specimens are properly prepared, and constantly inspected, poisoning is not absolutely necessary for private collections. There is, however, great danger of the introduction of insects through badly-prepared specimens received in exchange. I have never poisoned a specimen for my own herbarium, although my experience has extended over fifty years. Sometimes insects have been introduced in specimens received from other collectors; but it has always been found possible to get rid of the invaders without poisoning, although not before a small amount of injury has been done.
The herbarium of Wellington College was formed in 1874–75: the specimens were mounted on sheets of white paper, but were not poisoned, and, although but little used of late years, the collection is scarcely touched by insects, having been kept in an excellent air-tight cabinet.
The most troublesome insects in the colony are Anobium paniceum, L., which has become almost cosmopolitan; two small moths; and one or two Acari. Another small beetle, apparently a species of Ptinus, is only occasionally met with. Camphor freely distributed through the herbarium tends to deter insects, but is not an infallible preventive. Biological specimens attacked by insects of any kind may be thoroughly cleaned by exposure to the vapour of carbondioxide, which destroys even the eggs; but this remedy is a dangerous one, and can only be applied under proper precautions, while its effects are transitory. The best poison for plant-specimens is common methylated spirit charged to a little below the point of saturation with corrosive sublimate: if fully saturated, an efflorescence will be left on such specimens as Aciphylla, Ligusticum, Gentiana, & c., which absorb it freely.* Large Compositæ, Ranunculaceæ, Umbelliferæ, Cruciferæ, Leguminosæ, Liliaceæ, & c., are specially attractive to insects. Myrtaceæ, Pittosporeæ, arborescent Saxifrageæ, Myoporineæ, Glumiferæ, and Filicales are rarely attacked. The poison should be applied with a soft brush, such as is used by house-painters: brushes with metal attachments should be avoided: thick specimens may be dipped in the solution. Where numerous specimens have to be treated, guttapercha or vulcanite trays, or photographic dipping-dishes, will be found useful.
Specimens are occasionally fastened to the herbarium-sheets by sewing, a process not to be recommended. Strips of adhesive paper may be employed with advantage, or they may be attached by washing the undersurface with a solution of gum-arabic and tragacanth or with weak glue: common paste should be avoided. In no case should more than a single species be placed on the sheet, although the specimens may be numerous. The name of the plant should be written at the lower right-hand corner of the sheet, together with the locality in which it was collected, the date of collection, and the collector's name. If specimens from more than one locality are placed on the sheet the name of each locality should be stated under the proper specimen. A neat form of ticket may be adopted if thought desirable.
The different sheets of the same genus should be placed
[Footnote] * The mixture used at the Kew Herbarium is composed of corrosive sublimate, 1oz.; carbolic acid, 1oz.; methylated spirit, 1qt.
in a generic cover, which when folded ought to be ¼in. longer and broader than the sheets on which the specimens are mounted, and of rather stouter quality: the name of the genus, and, if the genus contain numerous species, the name of the sub-genus or section, should be written at the right-hand corner.
The genera must now be arranged under their respective natural orders in systematic sequence and placed in the herbarium cabinet, which, as already stated, should be airtight and dust-tight. A convenient size for the cabinet when demy paper is used is 36in. by 40in. and 21in. deep, outside measurement. This allows of twelve pigeon-holes 12in. by 8in. and 19in. deep. If sliding trays are required the width must be slightly increased. The outer edges of the cabinet should be bevelled inwards so as to allow of the doors being fitted as tightly as possible, and the hinges should fold backwards when required, so as to avoid projecting edges.
Mosses, Hepaticæ, and many Algæ are usually mounted on small sheets, which can be arranged in generic covers of the same size as that adopted for vascular plants: most lichens and hard Fungi should be mounted on small cards placed in shallow trays or drawers on account of the greater thickness of the specimens.