Let us make an in-depth study of Indian Herbarium. After reading this article you will learn about: 1. Meaning of Herbarium 2. Important Indian Herbaria 3. Purposes of Herbaria 4. Methods of Herbarium 5. Storage of Herbarium Sheets 6. Protection of Herbarium Sheets Against Molds and Insects 7. Role of Herbaria in Modern Taxonomic Research.
Meaning of Herbarium:
A herbarium is a collection of plants, which have been dried, pressed, mounted on herbarium sheets, identified and classified according to some approved system of classification. The succulent plants are usually preserved as such in some suitable preservative, such as 4% forma-line solution or F.A.A. Many types of dry fruits; cones of gymnosperms and inflorescences of palms, etc., are dried and kept in large containers.
About 1550, Cesalpini and his co-workers began quite definitely to preserve the materials they studied, and since then herbarium making became a great and interesting feature of botanical work. All civilized countries possess their own plant collections (herbaria).
The greatest herbarium of the world is at the Royal Botanic Gardens, Kew, England, possessing about six million specimens. A few good herbaria are there in our country. The biggest herbarium of our country is at the Indian Botanic Garden, Calcutta, possessing about one million specimens.
The herbarium of the Forest Research Institute, Dehradun has about 3, 00,000 specimens. The herbaria of Agricultural College and Research Institute, Coimbatore and National Botanical Gardens, Lucknow, have about 200,000 and 40,000 specimens respectively.
There are about 25,000 specimens in the herbarium of the Divisions of Mycology and Plant Pathyolog at Indian Agricultural Research Institute, New Delhi. The herbarium of the Division of Botany at I.A.R.I. New Delhi, contains about 3000 specimens.
Important Indian Herbaria:
1. Forest Research Institute (FRI), Dehradun:
The botany branch, one of the first to be created today comprises of three sections, viz., systematic botany, wood anatomy and plant physiology. The division today maintains a botanical garden, an arboretum, having one of the richest live collections of both indigenous and exotic tree species, and a bambusetum, containing germ plasm of forty species of indigenous and exotic bamboos.
All this provides a rich source of material for research, teaching and training.
Systematic Botany and Herbarium:
This section has been largely responsible for the collection and identification of a large portion of the floristic diversity of the Indian subcontinent. Started by Gamble (1890), the herbarium of the FRI has grown to become one of the largest of its kind in Asia.
It today houses 3,25,000 authenticated plant specimens, including 1300 type specimens, as well as a carpological collection. Some of the notable publications of the division, based primarily upon the herbarium collection, are ‘Manual of Indian Forest Botany’ ‘World Monograph on the genus Toona’, ‘Forest Flora of Punjab’, Kumaon, Chakrata, Andamans, Orchids of north-western India and food from Forests.
2. Herbarium of the Indian Botanic Gardens, Calcutta:
Foundation, 1787; Status, directed by the State of West Bengal, Department of Agriculture, Animal Husbandry and Forests; Number of specimens, more than one million Herbarium. World-wide, mainly phanerogams and ferns of India and neighbouring countries of South and South East Asia.
In addition to these there are some authentic collections of Cryptogams, Associated Botanic Gardens: Indian Botanic Garden, Calcutta, and Lloyd Botanic Garden, Darjeeling.
3. Herbarium of the National Botanic Gardens, Lucknow:
Foundation, 1948; in 1953 taken over by the Council of Scientific and Industrial Research (CSIR), New Delhi, Government of India. Status, C.S.I.R., Govt. of India. Number of specimens, about half million. The garden has been established by C.S.I.R., as a Central Garden for India.
4. Madras Herbarium, Agricultural College and Research Institute, Coimbatore:
Status, Department of Agriculture, Government of Tamil Nadu. Foundation, 1874. Number of specimens, about half million, Herbarium, world-wide, mainly Phanerogams. Important collections, collections of the flora of Madras. Associated Botanic garden. Botanic Garden and Research Institute, Coimbatore.
5. Herbarium of the Division of Botany, Indian Agricultural Research Institute, (I.A.R.I.), New Delhi:
Status, maintained by Government of India. Number of specimens about 10,000. Herbarium, North India, introduced plants of economic value, wild relatives of crop plants and associated botanic garden.
Purposes of Herbaria:
The drawings, photographs and descriptions of the plants cannot show, what is desired to show by them about individual variation and details of structure and development. In most cases it becomes necessary to compare descriptions with actual specimens which are found in widely separated regions.
Most comparative studies for taxonomic purposes are made in the herbarium and laboratory. The plant collections are much used for comparison with new material. The newly collected specimens are identified by the comparison of their morphology and the morphology of the plants collected in the herbarium.
Methods of Herbarium:
The specimens must be collected in every stage of their growth and reproduction and from different localities and habitats. The single specimen may be collected in the late flowering stage having both flowers and young fruits. A complete specimen possesses all parts of the plant including the root system.
In certain cases, the roots and other underground parts of the plant are necessary for identification. For collection of the plants one should go out on excursion several times in a season.
A list of instruments required by a plant collector, while on excursion is given here:
1. A pair of secateurs for cutting woody twigs;
2. A khurpi for digging up roots and underground stems;
3. A knife;
4. A pair of forceps;
5. A vasculum for keeping the collected plants and their twigs;
6. A wooden plant;
7. Blotting papers and newspapers;
8. A field book;
9. A pocket lens;
10. A small diary to write notes about plants and their habitat.
Pressing of the Plant Materials:
Generally the plants are pressed flat. To get good specimens, the plants must be pressed before their, wilting. Generally the plants are collected in a cork lined tin vasculum, and then they are pressed after the day’s trip. To get the finest specimens the plants must be pressed directly in the plant press, then and there, as soon as they are collected in the field.
Methods of Pressing the Plant Materials:
The plants are pressed in between the sheets of newspaper. These sheets are alternated between sheets of blotting paper. The wooden presses are too heavy to carry them in the fields, and therefore, while going on a collection trip the presses with aluminium covers are preferred. The field press remains tied with the leather straps.
The plants become dried by transferring their moisture into the blotting sheets. The weights are kept upon the press or the press is tied tightly with leather straps, so that, the wrinkles of the plant materials are without crushing the plant tissues. The standard size of the press is 12″ x 18″.
Drying of Plant Materials:
The blotting sheets or newspaper sheets which have been used for pressing the plant materials must frequently be changed after every 24, 48 or 72 hours. The changing depends very much upon the weather conditions.
Changing every 24 hours for two or three days and then two or three more times at longer intervals is a good rule, but this is too much for the plants of arid region. The succulent plants require changing more frequently, and they require a long time to become dry. The drying of some plants such as saprophytes (Monotropa sp.), succulent hydrophytes, and plants wet with rain or dew is very difficult.
Such plants become black during their drying process. This becomes necessary that the driers (blotting sheets, newspapers, etc.) must have changed twice or thrice in a day continuously for several days. Even the great care does not prevent the discolouration of some species.
Drying of Plant Materials with Artificial Heat:
Now a days, this method is generally used for drying of plants by plant collectors. Usually this method is employed in the damp climates especially in hilly regions during rainy season.
The method is as follows:
The specimens are pressed in the field press for 24 hours in usual way. The plants are then rearranged within the finely corrugated aluminium sheets. The press is then Strapped and thereafter, the heated dry air is passed over through the corrugations of the aluminium sheets.
These presses with plant specimens are placed in specially constructed ventilated boxes fitted with electrical incandescent light bulbs. The strapped press may also be placed in a hot air oven at desired temperature.
A small electric fan also be placed in the oven, so that the warm air may be forced through the corrugations of the aluminium sheets. Instead of electrical appliances, kerosene lanterns and stoves may also be used for the purpose.
Small and rare specimens may be dried quickly with an electric iron by keeping them in between layers of thick cloth or paper. The time required for drying the plant specimens by artificial heat ranges from 6 to 24 hours. Generally the plants are taken out from the press after 24 hours, and then they are transferred to an ordinary press.
Mounting of Specimens:
After drying, the plant specimens are mounted on herbarium sheets. The sheets must be of heavy white paper to give support to the plants in handling. The standard size of the herbarium sheets must be of good quality, so that it will not turn yellow or brittle with age.
The specimens are fastened to the sheets by glue or gummed cellophane tape. Usually one specimen, no matter how small it is, should be mounted on one herbarium sheet.
Labelling of the Specimen:
A label must contain as much information as possible about the specimen. It is then attached to the lower right hand corner on the herbarium sheet.
The label must contain the following information:
Now-a-days the ecologists show the effects of habitat on morphology and also the distribution of species according to habitat, and such data are only possible when the plant specimens are labelled very properly.
The Field Data:
There are two important methods for recording field data:
They are as follows:
1. While collecting the plants a plant collector keeps a field book. The field book contains the numbers, which correspond to the numbers of specimens collected. The ecological and other data about the collected plants must also be given in the same field book.
2. According to this method the printed forms with headings indicating the required information are put in convenient sized pads. While making collections each printed form duly filled is attached with a specimen, and then the specimen is pressed in the field press.
Storage of Herbarium Sheets:
After mounting the plant specimens on herbarium sheets they are usually kept in specially constructed herbarium cases. The wooden or steel cabinets with shelves slightly bigger than the size of the herbarium sheets are used for keeping the mounted plant specimens. The keeping of mounted plant specimen for further record is known as ‘filling the specimen.’
In comparison to wooden cabinets, the steel almirahs are being preferred as they protect the plants from being damaged by the insects and fire. The specimens are arranged in their cases according to any well-known taxonomic system of classification.
In our country and most of Commonwealth countries and British colonies the Bentham and Hooker’s system of classification is being used for this purpose. Engler and Prantl’s system of classification is also used to classify the plants in many countries.
The plants are being arranged family wise and an index card of the families is being prepared. Within the families, the genera are being arranged alphabetically. The specimens of one genus are placed in a folded genus cover. The species are also arranged alphabetically within the genus.
Protection of Herbarium Sheets Against Molds and Insects:
The mold fungi do sufficient harm to the plant specimens, if they are not well dressed by some effective chemical. For this purpose the plant specimens are sprayed with 2% solution of mercuric chloride which is highly poisonous. The insects do much harm to the specimens. To overcome this difficulty, various chemicals have been applied to the specimens.
The moth balls, and naphthalene flakes are being placed in the shelves of herbarium to check the insects. These act as repellents to the insects. The mixture of paradichlorobenzene acts as an effective repellent to the insects.
The other chemicals which are used as insect repellents are D.D.T. (i.e., dichlorodiphenyl- trichloroethane), carbon disulphite gas, (insecticidal fumigant) etc. The heat is also being employed to kill the insects. If the mounted sheets are being placed in suitably designed steel almirahs for four to six hours at 60°C, all the insects and their eggs are being destroyed.
Preservation of Type Specimens:
The type specimens are those on which the name of some taxon has been based. These specimens are those which are used by the author of a name as a basis for the name and description of a species and designed by him as a type specimen, and therefore, they are supposed to be so valuable that they are always preserved with special care.
The type specimens are handled with care and are kept away from regular specimens in separate steel cases by the curators. Usually such specimens are kept in separate cellophane envelopes.
Role of Herbaria in Modern Taxonomic Research:
Herbaria and herbarium taxonomists have contributed so significantly to our understanding of Natural History that there is no need to defend their existence. There is an urgent need to undertake extensive and intensive explorations of all parts of the country. This is possible and could be carried out very effectively if the Universities start taking an interest in developing herbaria.
Frequently the herbaria are called upon to perform certain duties. While public supported herbaria may be approached for identification of plant specimens and supply of information not easily available from public libraries.
Without active basic research identification of specimens may be often difficult or impossible. Hence the herbarium based botanists (taxonomists) should devote at least some time to carry out revisions and monographic studies of difficult groups of plants (K. Subramanyam and C.P. Sreemadhavan, 1970).
Designing of Modern Flora:
The species concept and the recognition of intraspecific categories need particular examination; in fact a rational process of taxonomic thought should pervade the entire work.
It should reflect adequately the current trends in taxonomic thought and practice and at the same time, keep itself within the limits of a well balanced, integrated botanical work-a creative work meant to inspire botanists of all disciplines and thus help to elevate systematics to its deserved place among the more sophisticated branches of Botany (M.A. Rau, 1970).
Phytogeny is the evolutionary history of a taxon, and attempts to account for its origin and development. The term phytogeny is the autonym of ontogeny.
Ontogeny differs from phytogeny in that it accounts for the life history of the individual plant from its development from the zygote to the production of its own gametes. A primary objective of phylogenetic studies in botany is the determination of origins and relationships of all taxa of both extinct and living plants.
Significance of Phylogeny to Taxonomy:
Phytogeny deals with the evolutionary history of all taxa. It is a function of taxonomic research at all levels of classification. The ultimate goal of phylogenetic research is the production of a phylogenetic system of classification. The phylogenetic system shows the genetic and time relationship of any one taxon to another.
According to Turril (1942), “taxonomy is based on characters, phylogeny on changes of characters.” A phylogenetic system of classification for plants would provide the answer to questions of (i) their origin (ii) to their modes of evolution, (iii) to problems of monophyleticism vs., polyphyleticism, (iv) the identity of primitive and advanced characters, etc. It would conclude in a single stable classification of relationships.