A herbarium is defined as a collection of plants that have been dried, pressed and preserved on sheets of hard paper. The dried plants are classified into separate groups and arranged for future reference especially for taxonomic studies.
A plant collector should needs to have the following
equipment :
(i) a gardener's knife, (Fig. 35.10a)
(ii) a plant press or vasculum, (35.10b)
(iii) blotting papers to dry plants,
(iv) trowel to dig the soil around surround the plant and uproot the plant,
(v) collecting and mounting sheets,
(vi) gum tape, labels, waterproof ink we use it because do not damage of pen marks due to water and pen.
1. Collecting botanical specimens
Fleshy plants lose their diagnostic features when dried so they are preserved in 4% formalin in glass containers. Gymnosperm cones and dry fruits ware collected and preserved as such.
Plants should be collected from various localities for the preparation of a herbarium. The herbarium should also have representative specimens from various groups of plants.
A complete specimen when collected must and should have all the parts including the root syst em. It is better to collect a plant at its flowering stage. Put A tag and give the location from where we collected. We need to collect About five or six specimens of each kind of plant should be collected. The plants that are collected are should either be pressed then and there or collected in a vasculum and pressed later. Vasculum is a metal cylinder with a sliding door in which plants are collected (Fig. 34.10b).
2. Pressing, Drying and Preserving
The collected plant should be pressed between sheets of blotting paper. One plant is arranged on one sheet so that its parts should not overlap. Specimens are longer than the sheets can be folded in the form of 'V or 'N'.
The plant between the sheets is put in a press for twenty four hours to forty eight hours. The press is now opened, blotting
sheets changed and plants rearranged again and put back in the press for another two or three days. The pressed specimen is then dried in sunlight or heat from some other source.
To prevent the abscission layer formation and decay, plants are killed (poisoned) with formalin or Mercuric chloride (HgCl2) or Carbon Tetra chloride (CC14). Also dipping in Mercuric chloride (HgCl2) saves them from attack by museum pests such as beetles. Fig. 35.10(c).
3. Mounting and Labelling
After drying, specimens are mounted on mounting papers or herbarium sheets which are usually of a standard size of 11.5" x 16.5" and strong enough to support the dried plants. We can be use Glue or by adhesive tape or adhesive paste is used to stick the specimens on to the sheets.
Each sheet should be carry a label pasted on the lower right hand corner giving the
(i) the site of collection, locality and altitude
(ii) name of plant
(iii) family
(iv) habit
(v) date of collection
(vi) ecological notes
(vii) name of collector.
Herbarium sheets should be stored in herbarium cases or steel almirahs. They should be arranged according to the system of classification. Moth balls, naphthalene flakes or 2% of Mercuric chloride should be sprayed to keep away from mould, fungi and insects.