Collection and preservation of Plants
The necessity of plant collection and the importance of Herbaria in particular has been greatly increased in these days due to the present human impact and changing environment. These negative trends often resulted in the disappearance of tropical and subtropical forests in many parts of the world. According to environmentalists, the number of plant and animal species disappearing now from all over the world is three or four times more than it was in the previous centuries. In Saudi Arabia, one of the reasons for the this extinctions is the fluctuations in the climatic change and the unsustainable use of its natural resources.
Well preserved plants in a herbarium are a great help for all botanists and enthusiasts who are engaged in the study of the flora of a country or a region. Collecting wild plants for scientific study of any discipline requires some sort of special skills. Following is an outline of the method of collection and how to preserve these plants for future study.
1. A field-bag to carry smaller items for immediate use such as notebook, number tags, polythene bags, paper bags, binoculars, camera, GPS, indelible writing pens or pencils, knives/scissors, Lap Tops computer (Optional), etc.
2. Field Press (if the field collection is meant for more than one day.). A field press consists of two end boards having 18 X12 inches size and 1 inch thickness, two strong webbing straps, preferably 1.5 m long and non-slip buckles. Double faced corrugated cardboards with corrugations at right angles to the long axis (18X12 inches), sufficient quantity of old newspapers and blotting papers
3. Number tags: This will be either tear-off portions of the pre-printed field books or ready made tags with twine attached to one end in order to tie the tag on the specimens. Each tag will carry a number which enables the collector to find out the description of the specimen from the field note book at a later stage.
4. Field book: Many features of the specimen, especially the shape and colour of the corolla, habit and habitat of the plant, etc, can not be detected from a dried specimen. the description in the field book will be a great help for the collector in identifying the plant than recollecting them from memory. A usual field book contains information such as Name of the specimen, local name, locality, collectors name, collection number, date of collection, soil type and a brief description about the plant.
5. Cutting implements like pruners, showel, hoe, axes, etc.
6. Polythene/paper bags of various sizes or metal vasculum.
Collecting the specimens
A botanical specimen may consists of one or more whole plants, complete with roots, stem, leaves, flowers and if possible, with fruits. If the plants are small, it is advisable to collect several specimens of the same plant from close proximity. In the case of large herbs, shrubs or trees, it is necessary to collect a portion of a twig with leaves and flowers/fruits as a representative specimen. The size of the specimen, if it is for preservation, depends upon the size of the sheet for mounting. Usual size of the herbarium sheet is 17X11 inches. After collection, the specimen is tied with a tag with a number (same as the number given for the description of the plant written in the field book.). Most of the plants wilt very rapidly after being cut or dug out of the ground. Previously, collectors used a metal box called vasculum into which the collected plants were placed for carriage to the field base or herbarium. Now the advent of polythene bags have become more convenient and can keep the plants fresh for more than 3 hrs. Sometimes the flowers or fruits are too large to be pressed with the leaves. In such cases, flowers or fruits may be kept separately in small polythene or paper bags, each containing the same number as the other specimen with leaves. A minimum of two specimens should be collected for every species (depending upon the size of the populations).
Once the collection is over, the next step is to press the specimens. This is the most difficulty part of the collection and is to be done as early as possible. In arid countries like Saudi Arabia, the specimens can be dried with the help of an ordinary press without using artificial heat. the ventilated drying press fro this purpose can be prepared as follows.
1. Place the two straps horizontally on a table or the ground with
buckles of the left. 2. Place one end board across the
strap. 3. Then place one or two corrugated cardboards on the top
of the end boards. 4. Take one of the specimens carefully from the
polythene bag. Make sure that the tag is still tied on to the specimen.
the specimen is then placed in the newspaper folder. While pressing,
make sure that the leaves are upside down to show the ventral side. the
leaves which are too large to fit on the herbarium sheet need to be cut
into parts or folded. Large, pinnately or bipinnately compound leaves
much be pruned to fit on the herbarium sheet. While pruning, the base of
the leaf-stalk should not be removed. This may help taxonomists who
examine the specimen at a later stage to get an idea of the position and
number of leaflets. If the flowers are too large or have deep tubular
corolla, it is advisable to split the flower longitudinally so that
their parts can be readily seen. Many fruits are difficult to press
satisfactorily because of their large size. Such fruits can be cut
transversely and longitudinally and press one half or part of it.
5. Place a blotting paper or corrugated cardboard over the newspaper
folder containing the specimen. 6. Repeat this method for the rest
of the specimens.
When the press has sufficient number of specimens with blotting papers and corrugated cardboards alternating with the newspaper folders, the other end board can be placed over it and tighten the straps evenly.
|The specimens have to examined periodically, preferably in every 24 hrs. the newspapers, if moist, are need to be replaced with new ones. While changing the newspapers, make sure that the number tag is still with the material and all the fragments such as flowers or fruits are also transferred to the new newspaper folder. This way moisture is absorbed from the material to absorbent by the simple process of diffusion. the used absorbents can be made ready for re-use by placing them outside during the day time or in a drier. During winter season an artificial drier will be helpful to speed up the removal of moisture from the specimens. This can be done by making a wooden box with metal net or a perforated sheet on the top side and two or three electric bulbs connected at the bottom of the box. The number of days that the materials remain in the press depend on the type of specimens. As a rule, a plant is ready when it is crispy and not cool when touched.
In many tropical and sub-tropical countries, poisoning the specimens is
another important step before mounting in order to prevent any possible
fungal or bacterial attack in future. the solution used for this purpose
consists of Mercuric Chloride, Ammonium Chloride and Ethyle Alcohol. The
quantity of chemical used at a time depends upon the number of specimens
to be poisoned. Dissolve 150 gms of Mercuric Chloride and 350 gms
of Ammonium Chloride in a little water as possible. To This add 10
litres of 96% alcohol. Applying the chemicals can be done by brushing it
gently on the specimens. After poisoning, the specimens may remain in
press for another day or two in order not to get the leaves and flowers
The next step is mounting. It can be mounted to any stiff paper of 17x11 inches size. Specimens can be mounted by using any non-toxic white glue available in the market or can be done by using narrow strips of adhesive tape either cloth or paper backed. Gluing, as the name implies, involves the attachment of the specimen to the mounting sheet by applying glue on the underside of leaves and twigs. After gluing, the specimen is mounted in the middle of the sheet and place small weight over it for some time. Fragments of the inflorescence, detached flowers, broken twigs or loose fruits can be put in a separate plastic or paper bag (5X5 cms) and pined or stick at the left hand corner of the herbarium sheet. This can be used for studying the specimen in the future. Finally comes the labelling. Usually the label (14X14 cms) is fixed at the right hand bottom corner of the sheet. A label consists of collection number, Latin name, Family Name, Vernacular Name, Habit, Habitat, Locality, Date of Collection and Collector's name. A small space may be provided at the bottom of the label to write notes of any special interest. In some labels, map of the country is also included in order to mark the locality of the plant from where it is collected.
Storing the Herabrium sheets: Most of the genera have more than one species. All these specimens can be brought together in a separate cover, called species cover. This should be of a different colour in order to differentiate it from the herbarium sheet. In some herbaria species covers are grouped together in a genus cover. The species covers should be clearly labeled with genus and species names and placed in the pigeon-holes of the cabinets in alphabetic order.