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Preservation of Specimens

The two main steps in preserving floral collections are pressing and drying.

Correct pressing prevents plant parts from curling or wrinkling during the drying process, and allows the requisite plant parts to be visible for identification.

Care in pressing specimens will result in more useful and visually appealing herbarium specimens. The process consists of laying the plant specimens in folded sheets of newsprint separated by cardboard

Sheets, and placing them in a pressing frame, which is then tightened with straps.

Drying involves an adequate length of time and exposure to ‘‘dry’’ air, and maintenance of the specimens in the press, e.g., changing the newsprint to speed up the drying process and cinching the press daily as the specimens dry

Preservation of plant specimens

Plant specimens should be preserved as quickly as possible soon after collection in order to maintain their characteristics  of the plant  as natural as possible . There are two main methods of plant preservation ie   chemical   and drying method

(a) Chemical method

 The plant specimen is preserved under a chemical preservative. These method is useful for preserving freshly succulent plants eg aloe vera . The plant after collection is put in jar  in as natural as possible  where chemical preservatives are added  and tightly closed to avoid  evaporation of the preservative. It should be completely filled with preservative to avoid  oxidation of the plant.

 In order to ensure the penetration of the preservative, the plant should be pricked to allow penetration of the preservative .most preservatives used are formalin and ethanol . The plant specimens have to be put in a fixative  before being put in a preservative

(b) Drying method – most plants stored in a herbarium are dry specimens. drying is hastened by pressing the plant between two sheets of bloating papers (adsorbent papers).

Plant pressing serves two objectives

1. a) To flatten the plants to avoid shriveling
2. b) To fasten drying ie to reduce drying time .

A plant press consist of a pair of frame 80x 45 cm. each made from wood . Currently, plant press are made from wire mesh  . In between the wire mesh or frames , is placed a bloating paper  where the plants are placed on very thin sheets of papers .

 The press is held with straps or strings or rubber bands  tightly over it . The bloating papers should be replaced every time (old newspapers can be used as bloating papers )

 The plant should be arranged on the bloating papers  so as to look as much  raw as possible  with leaves flattened and flowers displayed  to show different  views of florescent . Surplus leaves can be removed . Succulent plants must also be killed  by being presses since if dried in a normal way , they often continue to grow .Killing is done by immersing them  in methylated spirit  or alcohol for some hours  or put in paraffin  or boiling water  for 5-10 min  though the later method  adds water to the plant . Plants should be pressed as soon as possible

For herbaceous plants

• Place sheets of plants with high moisture content singly between cardboard separators, and check daily to see if the newsprint needs changing to facilitate drying.
• For trees and shrubs
• Bend or cut stems of larger plants to fit the sheet, or place them on separate sheets. Designate the parts a, b, c, etc., but use the same collection number.
• Place foam sheets top and bottom, or a small roll of paper on top of or alongside bulky or thorny plants to distribute the pressure evenly.

For aquatic specimens

The delicate structures of many aquatic species require special care and attention. Some aquatic plants do not have structural tissues to give them rigidity and they collapse when removed from the water. Fragile stems tend to stick to newsprint or break off the plants with excessive handling.

They need to be floated directly onto a sheet of thin mounting paper and arranged while the sheet is slowly withdrawn from the water.

• Partially fill a large sink, bathtub, or photographic developing tray with cool water. If you do not have a container, use the lake or pond where the collection was made.
• Float the plant in the water.
• Slide a herbarium sheet into the water under the plant. Check with the paper supplier to ensure that the paper you are using will not change shape when wet.
• Arrange the specimens in the water. Untangle feathery stems. Carefully lift up the sheet (with the specimens), letting the excess water run off.
• Place the sheet aside to drip dry before pressing. An old window screen makes a good support while the sheet dries.
• Place a piece of waxed paper or cheesecloth between the specimen and the newsprint to prevent sticking of mucilaginous plants like Chara and
• Brasenia (experimentation will determine which works best). Note that the arrangement cannot be altered once in place.
• Some bulky parts like Typha fruits, Nuphar flowers, and Cicuta douglasii roots need to be sliced longitudinally to make them flat enough to press.
• Thorny plants eg accasia should have its thorns broken or bend.

Drying

Drying is a crucial step in preserving collected plant material. To ensure that a specimen retains its color and does not become brittle or scorched, the moisture must be removed rapidly, while using only a moderate heat. Good air circulation will speed up the process. Make sure the corrugated cardboard still has air spaces in between and is not crushed flat with use.

• During warm, dry weather, tie the press onto the roof-rack if you are travelling by car. The air will flow through the lattice panels and the corrugated separators when the vehicle is moving.
• Place the press inside a well-ventilated vehicle parked in a sunny spot.
• Plants will dry reasonably well in a heated room in a week if you change the papers regularly
• The drying paper used should be changed on daily basis.

How to dry

1. The paper changing can be done  by keeping the press in warn dry place
2. The press may also be arranged over a source of heat so that warm air can circulate over the press. this reduces the drying time
3. An oven with its   dial  indicating warm terms can be used as a drier
4. Too much heat  should be avoided  since it results in the plant  being baked and becoming extremely brittle  and break when mounted
5. A small jiko  can be used for drying specimen in the field

All dryers require adequate ventilation above, below, and on all sides.

If using a homemade light-bulb dryer, place the pressing frame on top of the dryer. Leave at least 15 cm between the bulb and the press. The lightbulb dryer will dry most plants in 24 hours.

Warm air should flow through the corrugations in the cardboard and through the sheets enclosing the specimens.

Open the press periodically and check the specimens to ensure that they don’t become too dry, or begin to mildew.

A specimen is considered dry when it does not feel cool to the touch when the press has been open for a few minutes.

Many plants will shed seeds during the drying process. Package the seeds and mark the collection number on the package.

Cones can be air dried in their paper collection bags.

After the specimens are completely dry, carefully remove them from the press and store them in bundles protected on either side by cardboard sheets. Tie the bundles with string using the quick-release herbarium knot.

Seal the bundles in dark plastic bags and place a descriptive label on the outside. If necessary, the plants can be stored for several years in a cool, dry place before they are mounted. The plastic bag ensures that insects cannot get in or out, decreasing the chance of bringing an infestation to the collection.