This section is from the book "Sub-Alpine Plants Or Flowers Of The Swiss Woods And Meadows", by H. Stuart Thompson. Also available from Amazon: Sub-Alpine Plants: Or, Flowers of the Swiss Woods and Meadows.
Some hints on how to collect plants and dry and mount them for an herbarium may be useful to some readers, particularly as the subject is discussed either very briefly or not at all in most botanical books.
Plants can be collected and preserved in Switzerland, or any other extra-tropical country, much in the same way as in the British Isles. Specimens are usually put into a japanned or painted tin, commonly called a vasculum; while an ordinary large sponge-bag would in the Alps be found a useful adjunct or alternative, for it can easily be carried in the ruck-sack when on mountain expeditions, and is more convenient than a tin. Sponge-bags are light and fairly waterproof, and for many small fleshy plants, such as Saxifrages and Sempervivums, they are both convenient and handy. Some botanists, however, prefer to take into the field a light portfolio, furnished with leather straps and sheets of drying-paper, so that the plants, and particularly the more delicate ones, and those, like Veronicas, whose blossoms drop easily, can be put straight into paper, and sorted and rearranged in a proper press on returning to the house. We do not, however, much recommend the use of such a portable press, especially as it wastes time and is quite useless in wet or windy weather.
Many of the tins carried by young botanists are bought ready-made, and are too short. For ordinary purposes the tin should be about fifteen inches long, seven or eight inches wide, and about two and a half or three inches deep. It should have rounded edges, and the opening, which is on the broad side, should be large enough to admit average specimens without difficulty or needless doubling. The cover to the opening is attached by a couple of hinges, and it fastens at the side by a sliding wire bolt. If this should work loose and there be danger of the lid falling open when carried, the bolt can be bent the least bit out of the straight and it will then hold firmly. The plant-tin is most conveniently carried from the shoulders by a leather strap; but sometimes it has a thick wire handle at the top, which is convenient on occasion. On hot days the vasculum should be kept as much as possible out of the sun, for the metal gets very hot if exposed to brilliant sunshine. To combat this difficulty, or rather to prevent its consequences, the writer often lays the first delicate specimens in a bed of fresh green leaves placed in the tin.
If necessary these can be removed as the tin gets too full.
When a sponge-bag is not carried, it is often an advantage to have a smaller tin, such as is sometimes called a sandwich-tin, which will go within the coat-pocket. Small and delicate specimens can thus be carried, or it can be used for wet or dirty roots which might damage delicate flowers in the larger box.
A perfect specimen should have root, stem, leaves, flowers, and fruit - both young and mature if possible. If, as is often the case, the fruit cannot be obtained on the same plant with the flowers, it should be gathered separately from another. It is most important to get the fruit, and in a more or less developed state, for in some families, such as Cruciferce, Legutninosae, and Umbelliferce, it is at times impossible without it to determine a plant correctly. Good typical specimens should be selected, not necessarily the largest, but the most perfect and convenient in size. When possible a root-leaf or two should be collected as well as stem-leaves, but, of course, in many small plants most of the leaves will be root-leaves.
The sheets of paper upon which the specimens are finally mounted should not be less than about 15 x 10 inches, which is the size most cartridge paper cuts into, but 16 1/2 x 10 is still better, and this is about the size adopted in the Kew Herbarium, and quite large enough for ordinary purposes, though exceeded in several of the other great public herbaria.
When plants are not more than about fifteen inches tall it is better to put them into the tin and the press whole - not cut or doubled. When, however, a tall plant or shrub is dealt with, a good flowering branch should be cut off with several of the lower stem leaves, and the root leaves, if any, should be added separately, so as to give the complete habit as much as possible.
A notebook should always be taken into the field, in which the names, when known, of all the rarer and more interesting plants should be entered, together with date, habitat, locality, and anything of special interest worth recording. These notebooks form the basis of both the temporary and permanent labels referred to later. When in a foreign country it is sometimes desirable for botanists to enter the names of all the interesting species they come across in their walks, whether they keep dry specimens or not, for such notes are sometimes useful long afterwards, and it is astonishing how quickly such things are forgotten if not noted down.
A press is very simply made from two stout boards, about 16 1/2 x 10 1/2 inches, and of sufficient thickness not to warp. The boards are best clamped together by cross-pieces at the ends, in the manner that drawing-boards are made; and they are either furnished with strong leather straps - screws are not advisable or the pressure can be obtained by placing glazed bricks, boxes of pebbles, or heavy iron weights on top. Such automatic pressure is best, for it adjusts itself to the diminishing thickness of the contents of the press as the specimens dry. A press of this kind, or a pair of them, can be taken to the Continent without much trouble; but if a few plants only are to be collected, it would suffice to take a couple of pieces of thick millboard with either leather straps or thinner straps made of a kind of braid, or of the cloth that saddlers use, with buckles attached. Elastic bands are not recommended, for they break easily and cannot be adjusted like straps.
To separate half-dried specimens from fresh ones, and to keep the whole mass fairly level, and generally to hasten the process of drying, we have found a few thin wooden 'ventilators ' or frames the size of the press, made of cross-pieces of wood half an inch wide and one-eighth inch thick, very useful. Sometimes strong wirework frames or lattices can be bought, which answer the same purpose, or they could be used instead of the wooden boards to form an actual drying-press.