collet the leaves of various plants prepare a herbarium write a brief report on thier shapes ,size and vanation
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Answer:
A voucher herbarium specimen is a pressed plant sample deposited for future reference. It supports research work and may be examined to verify the identity of the specific plant used in a study. A voucher specimen must be deposited in a recognized herbarium committed to long-term maintenance. More information on herbaria may be found in our web document "Herbaria and Herbarium Specimens."
Why is voucher material needed? Plant classification is constantly changing. Shifts in species alignments and groupings are made as new evidence comes to light. Identifications are subject to change. Vouchers specimens help cross-reference these changes to previous research.
GETTING STARTED
Preplanning for the preparation of voucher specimens is crucial. Arrangements should include:
targeting collection locations and date periods to obtain useful specimens;
obtaining collection permits from appropriate agencies (this can take months); and
establishing official contact with government, herbarium, and research personnel in the area you will be working. This is required by law in most countries.
PRESSING AND DRYING PLANT SPECIMENS
Specimens are pressed in a plant press, which consists of a wooden frame (for rigidity), corrugated cardboard ventilators (to allow air to flow through the press), blotter paper (to absorb moisture), and folded paper, typically a newspaper (to contain the plant material). The plant press is tightened using straps with buckles or bolts with wing nuts. The objective of pressing plants is to extract moisture in the shortest period of time, while preserving the morphological integrity of the plant, and to yield material that can be readily mounted on herbarium paper (an acid-free cardstock) for long-term storage.
In order to fit on a standard herbarium sheet, a plant specimen should be pressed flat to no more than 11 X 16 inches. If the specimen will not fit those dimensions, it may be folded or cut into sections. Multiples of smaller plants may be pressed together in order to provide ample material for mounting and study. Small loose pieces, such as seeds, may need to be placed in a small paper packet inside of the newspaper. Large fruits or bulbs are often cut in half lengthwise or in slices prior to pressing. In order to insure rapid and thorough drying, extremely succulent materials such as cactus stems may need to be sliced open and some of the fleshy interior scraped out.
Each specimen should consist of a stem with attached leaves and, if at all possible, flowers and/or fruits. The roots of herbaceous plants should also be included. In the case of very large trees, shrubs, or vines, pieces should be selected to illustrate to the greatest extent possible the overall characteristics of the plant and the range of variation in flowers, leaves, and other structures. Each collection, i.e. gathering of a plant specimen, should be assigned a collection number. Data for each collection should be entered in a field notebook (see discussion of label data below) and the number should be written on the folded paper containing the specimen. Do not trust your memory for this information! If ample material is available, a minimum of three specimens should be pressed for each collection, especially if collecting in a region where the flora is poorly known. This will help facilitate the identification of the plants through the distribution of specimens to various herbaria and researchers. An ethical collector will insure that his/her collecting activities do not pose a significant threat to the survival of endangered species or habitats. Ethical herbaria will only accept legally collected specimens. See Florida Plant Collecting : Regulations and Permitting for some guidelines on collecting in Florida.