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secreting furrow pollen grains in sac sticky pad y: h 1

orchid pollinium nectar-

secreting furrow y: h 1

orchid pollinium

Wasp With Pollinia Attached

An insect follows a nectar-secreting furrow on a petal until it reaches the center of the flower. Pollinia are removed when they adhere to the insect following an "explosion" initiated by the insect bumping a sensitive point below an anther. When the insect flies to another flower, the pollinia on its head catch on the sticky surface of the stigma and are pulled off at the same time new pollinia are being attached.

mechanism 2

Orchids pollinated by butterflies and moths may have a clamp at the base of the pollinia. When an insect inserts its tongue down the throat of the flower and touches a sensitive area, the clamp attaches the pollinia to the insect's tongue.

mechanism 3

Figure 23.18 Some pollinating mechanisms in orchids.

footnote on page 338. The specimens that comprise the bulk of the holdings of most herbaria, however, consist of vascular plants, and what follows pertains primarily to such plants.

The moisture content of flowers and other plant parts to be preserved should be reduced as quickly as possible, with a minimum of distortion. This is usually done with the aid of a plant press (Fig. 23.19). This simple device consists of two pieces of plywood (or other wood materials or thin metal plates) with dimensions of approximately 30 x 46 centimeters (12 x 18 inches) and a pair of webbing or leather straps to go around the boards. A number of felts (sheets of heavy blotting paper) of similar dimensions are placed between the boards. A folded page of newspaper is placed between each blotter, and a few sheets of stiff cardboard are interspersed between the blotters.

See d Plants: An 455

pollinium pollinium

Steps Budding Plants

stigmas throat pollinia immediately after removal from the flower stigmas throat pollinia a few seconds later pollinia immediately after removal from the flower pollinia a few seconds later

In the showy orchids, there are two separate stigma patches. When an insect visits a flower, the pollinia are attached to its head; then they twist outward and forward so that when the insect visits another flower, the pollinia are simultaneously deposited in the separate stigmas while new pollinia are attached to the insect's head.

mechanism 4

Bucket Orchid Pollination Process

One genus of orchids native to Europe and North Africa has a petal modified to resemble a female wasp. Male wasps try to copulate with the "female" and, in doing so, bump a sensitive area containing pollinia. The pollinia are "glued" to a wasp's head in the process and carried to another flower. The wasps thus effectively bring about cross-pollination.

faucet glands bucketlike petal partly filled with fluid mechanism 6

faucet glands bucketlike petal partly filled with fluid


trapdoor stigma

The bucket orchids of South America have faucet glands that partially fill a bucketlike petal with fluid. In visiting the flower, the insects may fall into the fluid. They escape by a trapdoor. The pathway of an insect assures contact with both the stigma and anthers containing pollinia, since they are located adjacent to the trapdoor.

Any soil clinging to the roots of a specimen to be pressed is washed off, and the plant is laid out on one of the newspaper sheets. Leaves are carefully straightened out, as are petals and other plant parts, so that they are not folded during pressing. Notes on where, when, and by whom the specimen was collected are penciled on the newspaper, or a number corresponding to such notes in a separate field notebook is used. The newspaper is then folded over the specimen and placed between two blotters (felts).

Many specimens may be placed in a press at one time or, if there is space, between the same sheets of newspaper. Only one species should be placed in a single fold of newspaper, however, as mixing species invariably leads to some being pressed better than others, due mostly to the varying amounts of woody tissues within the stems. If the plant is small, press the entire plant, and try to have both upper and lower leaf or flower surfaces visible. If, however, the plant is large (e.g., a tree) press representative parts, especially flowers and/or fruits. After the newspaper and specimen are

456 Chapter 23

Figure 23.1Q A plant press.

returned to the press, the straps are tightened around it as much as possible, and it is left to dry in the sun or near a heater (but not close enough to scorch!) for 3 or 4 days. Unless the leaves were succulent or wet at the time they were placed in the press, they should be dry enough to mount on paper at this time. If a press is not available, plants may be pressed between newspapers and blotters by placing heavy weights on top of them.

If possible, 100% rag-content paper should be used for mounting the specimen, as papers made from wood pulp deteriorate with age. The paper also should be thick enough to support the now-brittle specimen. The pressed plant(s) may be attached to the paper in one of several ways. Some workers spread a good white library glue on a glass plate and then place the specimen on the wet glue so that one side is covered with it. They then transfer the specimen to herbarium paper that normally measures 29 x 42 centimeters (11.5 x 16.5 inches). Others place the specimen on the paper first and add glue or liquid plastic at strategic points. The bottom right-hand corner of the paper should be kept clear for a label indicating the scientific name of the plant, collection information, the collector's name, and the collection date (Fig. 23.20).

Professional botanists also number their individual collections, giving a collection number after the collector's name. The label should measure about 7.5 x 12.5 centimeters (3 x 5 inches), and its paper should also be of 100% rag content. Specimens are then placed in manila folders and stored in some systematic fashion so retrieval of individual specimens is easily accomplished. Major institutional herbaria usually arrange the plants by families in a presumed evolutionary sequence, and then the genera and species are alphabetically arranged within the families. Paradichlorobenzene, mothballs, or similar material should be added to the cabinet or storage area to prevent insect damage during storage.

Although other forms of flower preservation are not associated with herbaria or professional botanical activities, a few will be mentioned here simply for reference. For example, some people are interested in pressing flowers for use in dry arrangements on cards, place mats, or other decorative items. In such cases, the pressing is done as though they were herbarium specimens, but the material is then further manipulated in one of several ways. For wall art, the specimens can be mounted on a piece of smooth cardboard, covered with clear plastic or glass, matted, and framed (Fig. 23.21). Decorative notepaper can be made by placing pressed flowers on the paper and covering them with rice paper or facial tissue. A mixture of one part white glue to three parts water is then brushed over the tissue, causing it to become a permanent mount, with the specimen clearly visible through the thin paper film. Clear contact paper cut to the appropriate size makes a good mount for pressed flowers placed on cards or place mats. Pressed flowers can also be embedded in clear plastic poured into molds.

Flowers can also be dried without pressing. With a little patience, relatively lifelike three-dimensional preservations can be made, although flowers with petals that are not easily detached lend themselves more readily to three-dimensional drying than others. Most such drying is done in a shoe box, but almost any type of container can be used. The bottom of the box is covered with about 2 centimeters (0.8 inch) of sand, silica gel, or borax mixture. The fresh flower, with a little of the peduncle or stem still attached, is then gently laid on the surface. After this, more sand, silica gel, or borax mixture is slowly drizzled by hand into the box until the entire flower is buried, with care being taken not to create air pockets around any parts (Fig. 23.22).

Each of the three drying agents mentioned has certain advantages and drawbacks. Sand must be thoroughly washed several times to be certain it is perfectly clean before use. The sand also needs to be completely dry, uniformly fine, and if possible, have individual grains that are relatively rounded rather than angular. Such sand with rounded grains is found around the Great Salt Lake in Utah and is available in arts and crafts stores. It takes about 2 weeks to dry most flowers with sand. Silica gel is also available commercially and is the quickest drying agent of the three mentioned, usually completing the job in 4 to 5 days (if the box is placed in a microwave oven, the drying process may be completed in as little as 5 minutes). Its granules tend to be of different sizes, however, giving the flower surface a slightly irregular texture. It also tends to darken certain colors, and it is expensive. When borax is used, two parts of it should be mixed with one part sand or cornmeal. It dries flowers in about 3 weeks but is sometimes difficult to remove completely from the dried flower surfaces.

When drying has been completed, the container is tilted, and the sand or other drying material is slowly and gently poured out in an uninterrupted motion. If any petals have come loose, they may be glued in place later. Wire may be inserted in the stem to add rigidity, and after any clinging granules have been carefully removed, soft, powdered colored chalk may be dusted on to restore any fading of color. It is recommended that beginners use fairly large flowers whose petals are not easily detached (e.g., zinnias, rose buds) for their first attempts at three-dimensional flower drying.

Seed Herbarium Design
Figure 23.20 A mounted herbarium specimen.

458 Chapter 23

Pressed Flower Wall Art

Figure 23.21

Pressed flowers framed as wall art.

Figure 23.21

Pressed flowers framed as wall art.

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