In this article we will discuss about:- 1. Meaning of Herbarium 2. Equipment for Preparing Herbarium Seeds 3. Method of Specimen Collection and Mounting 4. Uses 5. Important Herbaria 6. Identification of Species.
Meaning of Herbarium:
Herbarium is a place where dried and pressed plant specimens, mounted on sheets are kept systematically according to a widely accepted system of classification.
Herbarium is a repository or store house for future use. Every institute teaching botany, school college or university, has a small or large herbarium. Very large herbaria are maintained by botanical gardens and institutes connected with plant systematics. Every student of botany is required to collect plant specimens and prepare herbarium sheets.
Equipment for Preparing Herbarium Seeds:
Digger and pruning knife, sickle with long handle, vasculum, polythene bags, magazines or newspapers, blotting papers, plant press, field notebook, herbarium sheets, glue, labels, small transparent polythene bags.
Method of Specimen Collection and Mounting:
An area is selected for botanical excursion. It is preferable to visit the same site in different seasons. For herbaceous species the entire plant with intact parts is collected.
For others, shoots having flowers, leaves and fruits are selected and cut with the help of pruning knife. Sickle with long handle is used if the desired twigs are present at a height. Diggers are used to obtain underground parts like root system, tuber, bulb, corm, rhizome, etc.
The collected material can be placed in polythene bags or vasculum. Vasculum is a special box with a length of 45-60 cm, depth of 25 cm and width of 20 cm. It keeps the material airtight and prevents wilting till the same is placed inside drying sheets.
The collected specimens are spread over magazine or newspaper sheets. Care is taken to spread the leaves properly and to separate the petals so as to expose the essential organs. If the specimen is longer than the sheet, the same can be gently bent in n or w form. Some of the flowers are kept open so as to facilitate examination of floral parts. Some of the leaves are bent to expose dorsal (under) surface.
Magazine and newspaper sheets are now put inside the press. Plant press consists of two boards with straps for tightening. Details of collection should be jotted down in the field notebook. For this every collected material is given a number.
The details include plant size, branching, and root system and specialised underground organ, flower colour, topography and date of collection. Preservative liquid used for storing fleshy organs is FAA (10 ml. formalin, 5 ml. glacial acetic acid, 50 ml. of 95% ethyl alcohol and 35 ml. of water).
After 24 hours, the sheets are changed. Blotting papers can be used. They help in quick drying. Two or three changes are required at an interval of 3-5 days for complete drying of the specimens. Some workers prefer to maintain the specimens in drying sheets for 1-2 months. Meanwhile herbarium sheets are selected. They are available in different colours. The general size is 30 x 45 cm.
It is slightly shorter in American herbaria (29 x 41 cm). Good quality glue is applied to the back of dried specimen and the same is placed over the herbarium sheet.
Students prefer to use cello tape but the same should be avoided as its retaining power is little. Labels (7 x 12 cm) are fixed over the lower right hand comer of the sheets. Information about the family, genus, species, author, plant characteristics, area, date and collector’s name is given over each label.
The sheets are now covered with polythene or tissue paper in order to avoid tearing of delicate parts. Heavy parts like fruits or seeds are kept in a paper or polythene packet and attached to the sheet. Herbarium sheets are arranged according to a system of classification, e.g., Bentham and Hooker in India.
The specimens belonging to the same genus are often packed together and placed in steel cabinets. The specimens are treated with 0.1% mercuric chloride for preventing fungal attack. DDT, naphthalene and carbon disulphide are also used as pesticides. Repelling chemicals (e.g., Moth or naphthalene balls) are placed along with herbarium sheets for protection against insects.
Uses of Herbarium:
(i) It provides information about the local flora as well as flora of distant areas,
(ii) Herbaria are used for correct and authentic identification of unknown plants,
(iii) It provides information about the ecology of different places,
(iv) The information is useful in locating wild varieties and relatives of economically important plants. The same is helpful in breeding programmes for evolving newer and better varieties,
(v) It depicts the morphological variations found in species,
(vi) Information is obtained as to the season of flowering of various plants,
(vii) It serves as a quick referral system for taxonomic studies.
Important Herbaria:
Identification of Species:
Manuals, floras, monographs, catalogues and keys are used in identification of species.
Manual:
It is handy book containing instructions as to occurrence, collection and identification of species found in a particular area.
Flora:
It is a book containing information as to the habitat, climate, seasonal changes, distribution, description and index of plants found in a specific area.
Monograph:
It is treatise having all information about a particular taxon like family or genus.
Catalogue:
It is list or register that enumerates methodically all the species found in a particular place, often with brief description aiding identification.
Key:
It is booklet containing list of characters and their alternates which are helpful in identification of various taxa— class, order, family, genus and species.