*(contributed by J. R. Massey from Chapter 18 in Vascular Plant Systematics by A. E. Radford, W.C. Dickison, J. R. Massey and C. R. Bell, Harper and Row Publisher, 1974; used with permission of the authors)
Herbarium specimens are permanent records of a species (or population) as it occurred at a given time and place. The future value and use of any specimen is largely dependent on the care with which the collector selects, collects and prepares his spec imens. The following directions and suggestions on specimen preparation, field equipment and field records are given to assist collectors in preparing high quality herbarium specimens accompanied by adequate field notes.
I. Collecting Objectives and Planning
II. Supplies and Equipment
III. Selection of Material
IV. Pressing Plant Specimens
V. Field Storage of Specimens
VI. Drying Field Collections
VII. Data to Accompany Specimens
VIII. Identification of Collections
I. Collecting Objectives and Planning.
The specimens to be collected depend on the objectives of the collector, and the types of material to be collected will determine the techniques used, amount of material collected, and type of field data recorded. The following suggestions can greatly ai d the collector in getting maximum benefit of valuable field time.
- Outline objectives for a specific expedition.
- Prepare a list of all equipment to be utilized on a field expedition.
- Obtain localities from herbarium specimens, if specific materials are needed. It is best, when possible, to have several localities in the event some areas have been disturbed. Check flowering and fruiting dates on the specimens in the herbarium.
- Check local weather conditions and seasonal progress in the areas to be visited.
- Collect duplicate specimens (replicates) except in the case of very rare or protected plants (check state laws and conservation lists). Other plants to be avoided include those noxious weeds or parasites and their host plants under state or federal quarantine. Duplicates provide sufficient material for dissection or, if needed, verification by a specialist.
- Prepare voucher specimens (typical herbarium specimens) when collecting materials for cytological, anatomical, and other studies.
- Obtain collecting permits and other necessary permission in advance, if possible, if a trip is planned to a specific area such as a national park, foreign country,or other area. It is also advisable to obtain permission for collecting on private la nds whenever possible.
- Collect and document as many different species as possible in floristic studies. Do not overlook the inconspicious (so-called belly plants) or those plants which are difficult to collect or identify. Collect thoroughly in each habit.
II. Supplies and Equipment
- Field press: A press typically consists of two hardwood frames, with each frame made as follows: 4 wood strips 3/4 x 1/4 x 18 inches, and 5 wood strips 3/4 x 1/4 x 12 inches. The five short strips should be equally spaced on the 4 longer s trips which are also equally spaced and nailed, or riveted securely at the intersection of the strips. The completed frame should be 12 x 18 inches. Repeat for the second frame. Some collectors prefer the cheaper and often stronger 12" x 18" plywood pres s boards cut from 3/8" fir plywood. A number of types of presses may be purchased from biological supply houses.
- Driers (blotters): Excellent driers may be made by cutting sheets 11 x 16 inches from light-weight builders deadening felt (unsaturated) or from heavy blotting paper. Driers are also available from biological supply houses.
- Newsprint: Cut paper 22 x 16 inches and fold to 11 x 16 inches. Many use newspapers as found on the newsstand but unused newsprint may be purchased in rolls from local printers. Biological supply houses usually offer prec ut papers.
- Press straps (webbing straps): A pair of strong web straps (parachute or cinch type) with claw buckles are excellent for field purposes. Sash cord or rope is often also used. The minimum length for press straps is four feet.
- Field notebook: A pocket-size book which will not disintegrate when wet and pencil or pen with water-proof ink are necessary items. Some prefer to keep two books--one taken to the field and another which remains in a safe place and into whi ch field notes are copied. If field labels are used, one is placed in the paper with the specimen and a copy kept by the collector. Field notebooks should be permanent.
- String tags: Waterproof string tags are useful for labeling plants which are not pressed immediately following collection.
- Diggers and clippers: Both pruning shears or garden clippers and digging tools are necessary. A trowel (preferably with a steel shank), geologist pick, dandelion digger or heavy sheath knife are excellent for field use. A small trench shov el and pocket knife are also useful.
- Hand lens: For field observations and identifications a small 5x or l0x lens is desirable. These are generally available from bookstores and biological supply houses.
- Collecting bottles: Glass or plastic bottles with leak-proof screw caps are often desirable for collecting some materials. The size used depends upon the materials to be collected. Small vial-type bottles are ideal for collecting floral bu ds, flowers for clearing and other materials to be preserved in liquid preservatives.
- Liquid preservative: The type of solution used will, of course, depend on future use and type of material. For general anatomical purposes and materials such as wood, leaves, flowers and the like a mixture of Formalin-Acetic Acid-Alcohol (F AA) is widely used and may be prepared in the following manner:
Ethyl alcohol (70%) 90cc. Formalin (commercial strength) 5cc. Glacial Acetic acid 5cc.
Cytological materials are often fixed in a 6:3:1 mixture of Chloroform, 95% ethyl alcohol and glacial acetic acid or in Carnoy's Fluid (3:1 absolute ethyl alcohol and glacial acetic acid). Carnoy's containing 95% ethyl alcohol is useful for clearing leav es. (See Chapter 7). When using the 6:3:1 mixture the glacial acetic acid should not be added until materials are ready to be fixed. After materials have been in fixative for 24-48 hours, the fixative should be discarded and materials stored in 70% alco hol. At Kew, a solution of 50% alcohol, 5% Formalin, 5% glycerol and 40% water is used for storing plant materials. Each vial should contain a field label. Use pencil and slips of bond paper; the numbers should correspond to those in the field notebook.
- Vascula and collecting bags: Plant materials not pressed in the field immediately may be stored in a metal container (vasculum) in folds of wet paper. Due to the cost and bulkiness of this container many now prefer to use plastic bags (turkey or fertilizer) or rubber-lined canvas bags (military laundry bags). Local conditions will determine in part the type of bag to be used, but avoid exposure to sun, particularly if clear plastic bags are used. All materials should be carefull y labeled to avoid confusion when materials are pressed.
- Waxed paper: A roll of waxed paper available in supermarkets is useful in pressing many plants, particularly those that are viscid or which deliquesce. A single sheet placed over the material can greatly facilitate the removal of mat erials from the pressing paper.
- Manila coin envelopes: Small coin envelopes are excellent for collecting seeds, individual flowers, leaves, pollen, pollinators and other materials which cannot or should not be pressed. These should always be carefully labelled with the co llection number.
- Trays, cans, jars for living materials: It is often desirable to collect living materials for experimental work in the garden or greenhouse. A variety of containers may be used and will depend on the type of material to be collected an d the length of time materials must be stored.
- Cardboard storage boxes: Merrill cases or other cardboard containers which can be purchased flat make excellent storage for dry materials removed from the press in the field. It is advisable to use an insecticide or repellent if materials are to be stored for an extended period of time.
- Insecticides and repellents: Moth crystals or flakes (naphthalene or paradichlorobenzene) may be used as repellents. Considerable quantities of paradichlorobenzene in an air-tight container may be used as an insecticide. An excelle nt treatment is to place PDB in the folds of the specimen paper, tie specimens into bundles, and seal in a plastic bag.
- Maps: Highway, topographic, and geologic maps are often very useful in locating localities for particular species. Detailed county road maps can be obtained, usually at modest cost, from the state highway departments.
- Camera: Photographs are of considerable value when collecting woody or other materials where entire plants are not pressed.
- Color Charts: Several color charts are available for determinion of flower colors in the field, e.g., Horticulture Society Color Chart, Nickerson Color Fan, Horticultural Color Chart, etc.
III. Selection of Material.
Vigorous, typical specimens are to be selected. Avoid insect damaged plants as well as exceptionally small or large plants. Specimens should be representative of the population, but should include the range of variation of the plants, not those that best fit the press. Roots, bulbs, and other underground parts should be carefully excavated and the dirt removed with care. In most cases flowering and/or fruiting materials are necessary for identification purposes. Many collectors prefer to add extra flowers and fruits to their collections when possible to avoid dissection of the specimen proper. Plants too large for a single sheet may be divided and pressed as a series of sheets (see discussion below). In collecting large herbs, shrubs and tr ees, different types of foliage, flowers and fruits should be collected from the same plant. Collect sufficient material to fill an herbarium sheet and still leave enough room for the label. Bark and wood samples are often desirable additions when colle cting woody plants. Proper identification of many plants depends on several different characteristics--some roots, others seeds or mature fruits, some flower color (which should be noted in the fieldbook).
The following suggestions which are largely adapted from DeWolf (1968), Fogg (1940), and Fosberg and Sachet (1965), and Smith (1971) are given to assist in the selection and collection of particular kinds of plants.
Table 18-1, MATERIALS FOR IDENTIFICATION PURPOSES Taxon Essential or desirable materials for identification purposes Suggestions for note-taking and pressing Acanthaceae Fruits and flowers important. Flowers often detach easily after collecting. Agrimonia Underground parts useful. Press immediately Alismataceae Flowers and fruits (essential). Note presence of perfect and/or staminate and pistillate flowers and position of fruiting pedicels. Allium Flowers, seeds, bulbs (with coat) Amaranthaceae Ripe fruits (essential in some). Note whether plants are monoeicious,or dioecious. Collect both staminate and pistillate plants when possible. Amelanchier Flowers, fruits and leaves from same plant necessary. Note habit (erect or stoleniferous) Annonaceae Flowers necessary (these may open precociously and then grow considerably before and during anthesis) Apiaceae (Umbelliferae) Mature fruits and basal leaves. Araceae Fruiting material alone of little value; flowers, inflorescences and underground parts of great value; also leaves (often dimorphic) Peel epidermis away on one side to speed killing and dr ying or use alcohol or formaldehyde to kill and preserve in the field. Note glaucescence, sap color, vesture. For large aroids see suggestions in Frosberg & Sachet (1965). Araliaceae Flowers and fruits. Arecaceae Flowers and fruits, inflorescence axis and bracts, leaves, petiole, leaf base, notes on stem. See Tomlinson (in Frosberg and Sachet, 1965) for details on collecting suitable specimens. TD TD> Asclepiadaceae Flowers and fruits. Note flower color, number of leaves and arrangement, latex color, fruiting pedicels (erect or deflexed). Asteraceae (Compositae) Ripe fruits and flowers, basal and median cauline leaves and underground parts. Note color of ray and disk flowers; press some heads exposing upper surface and others with lower surface exposed. Split heads and press. Balanophoraceae Tuber surface important. Plants sometimes dioecious. Balsaminaceae Flowers and fruits desirable. Flowers fragile and tend to agglutinate on drying under pressure. Liquid preserved flowers desirable. Note flower color and markings. Bamboos Flowers and fruits rare but desirable. Culm sheaths from mid-culm nodes, portion of culm and branch, rhizome. Record node number (starting at base of plant) from which material is taken. Collect from 4th to 5th node. (See suggestions of McClure in Frostberg and Sachet for additional handling) Begoniaceae Both staminate and pistillate flowers and ripe fruits. Careful notes on colors, plants fleshy & oftendarken on drying. Betula Fruiting catkins essential. Notes on bark desirable Boraginaceae Flowers and ripe fruits. Split and press some flowers flat. Brassicaceae (Cruciferae) Flowers and fruits desirable; underground parts and rosettes. Burseraceae Fruit. CactaceaeFlowers, stem with grooves, tubercles and spines including both tranverse and longitudinal sections. Stems may be dipped in boiling water or formalin to kill tissue & allow more rapid drying. Handle carefully (preferably with gloves & forceps) but do not remove or cut all spines. Campanulaceae Flowers.Corolla shape important. Make careful notes and/or drawings. Capparidaceae Flowers desirable (these open precociously and then grow considerably before and during anthesis.) Caprifoliaceae Ripe fruits. Carex Mature perigynia, underground parts. Caryophyllaceae Flowers and fruits. Note number of styles and corolla color. CasuarinaceaeStaminate and pistillate flowers and ripe fruit. Dioecious or monoecious. Celtis Mature fruits. Coccoloba Leaves from adventitious shoots and from mature twigs; staminate and pistillate inflorescences. Commelinaceae Flowers, spathe, underground parts. Flowers should be pressed between tissue & waxed paper and/or preserved in liquid. Note corolla & anther color. Spread spathe & press flat. Convolvulaceae Flowers and ripe fruits desirable. Split flowers and dry flat. Note corolla color and markings. Cornaceae Mature fruits. Note color of branchlets and pith Crataegus Flowers and fruits from same tree. Note anther color. Cucurbitaceae Flowers and ripe fruits. Dicecious or monoecious. Note corolla shape and color, and color of mature fruits. Cuscuta Flowers and fruits. Note nature of petals & their appendages, shape of fruit and host. Cyperaceae Ripe fruits and underground parts. Dilleniaceae Ripe fruits. Dioscoreaceae Staminate and pistillate inflorescences, axillary bulbils, underground parts and base of aerial stem; mature fruits if possible. Note direction of twining of stems.< /TD> Dipterocarpaceae Ripe fruits. Epacridaceae Ripe fruits. Ericaceae Flowers and fruits. Note flower color and waxy "bloom" on fruit. Euphorbiaceae Staminate and pistillate flowers, ripe fruits. Note color of glands. Sap may cause dermatitis. Fabaceae (Leguminosae) Flowers and fruits essential; underground parts desirable. Note flower color. Fagaceae Ripe fruits, mature leaves. Collect staminate & pistillate flowers when possible. Note shape & size of plant. Fraxinus Ripe fruits nearly essential, staminate and pistillate; flowers desirable. May be dioecious Galium Fruits often essential; underground parts. Note flower color & habit of plant (erect or reclining). Gesneriaceae Flowers and fruits. Note colors, plants often fleshy and darken upon drying. Gnetaceae Flowers and fruits. Dioecious or monoecious. Hydrocharitaceae Flowers and fruits Note position of flowers (floating or submerged). Iridaceae Flowers and mature fruits, underground parts. Press flowers immediately & use tissue and waxed paper Isoetes Fertile specimens. Note habitat & whether plant was emersed or submerged. Split some plants vertically. Juglandaceae Fruits, leaves. Note bark characters, size and shape of tree Juncaceae Fruits. Note number of stamens, shape of leaf (flat or terete), expose ligule Lamiaceae Flowers and mature nutlets, base of stem and underground parts. Split open some flowers & press flat; note flower color & markings. Lemnaceae Flowers and fruits desirable. Note number of roots per "frond". Float specimens out on paper, place in packets. Lepidium Flowers and fruits Note presence or absence of petals. Liliaceae Fruits alone useless, flowers and underground parts most desirable. Note if leaves are flat or round. Make longitudinal section of bulbs; leave bulb coats intact. Loranthaceae Flowers and fruit. Note fruit color & host plant Malvaceae Flowers & mature fruits, underground parts helpful. Note flower color, split open some flowers & press flat. Melastomataceae Flowers and fruits Petals fugacious. Menispermaceae Staminate & pistillate flowers; fruits desirable. Dioecious Moraceae Fruits desirable. Frequently dioecious, note fruit color. Musaceae Axis of inflorescence and ripe fruit. Photograph entire plant when possible. Myristicaceae Ripe fruits desirable. Dioecious. Myrtaceae Fruits. Najadaceae Fruits. Float specimen out on white paper. Nepenthaceae Pitchers of full grown cauline leaves essential. Orchidaceae Flowers and fruits; fruits alone almost useless. Note flower color, markings, & fragrance. Preserve some flowers in liquid. Orobanchaceae Ripe fruits desirable. Note host plant. Pandanaceae Ripe fruit, leaf tips Note stem diameter; photograph or habit sketch very desirable Picea Mature cones. Note color of foilage. Piperaceae Fruits. Note colors (plants often darken on drying. Poaceae (Gramineae) Mature fruits, underground parts and stolons. Note anther color. Press clums to show sheath & ligule. Polemoniaceae Flowers, fruits and underground parts. Note flower color & split corollas open and press flat. Polygalaceae Flowers and fruits and seeds; underground parts. Note color and habit, leaf, dimorphism, if not pressing entire leaf. Polygonaceae Fruits and underground parts. Potamogeton Fruits and stipules. Press so stipules are clearly displayed. Pteridophyta Fertile fronds, rhizome or rootstock, sterile fronds if different from the fertile. Tree ferns - petiole, leaf bases and leaf scars. Ranunculaceae Fruits and underground parts. Ribes Flowers and fruits. Note color of fruits. Rosaceae Fruits; flowering and sterile shoots. Note habit of plant. Rubiaceae Fruits very desirable. Rubus Habit important, twigs of sterile and fruiting branches. Note if canes are arching or not, rotting at tip or not. Salix Mature staminate and pistillate catkins and leaves from the same plant. Dioecious. Sapindaceae Fruits desirable. Sapotaceae Fruits desirable. Scrophulariaceae Flowers. Split flowers & press flat, make careful notes on color & markings, note host where applicable, many must be pressed immediately; commonly darken on dry ing. Note host where applicable. Smilax Fruits and vegetative material. Note fruit color & whether main axis is smooth or spiny. Solanaceae Flowers and fruits. Split open some flowers & press flat. Styracaceae Fruits desirable. Symplocaceae Ripe fruits. Utricularia Flowers, fruits, leaves. Float plants out on white paper, spread leaves. Excavate terrestrial species carefully. Vaccinium Flowers, fruit. Note fruit color and plant habit. Viburnum Ripe fruit. Zingiberaceae Inflorescence and underground parts Inflorescence best preserved in liquid.
IV. Pressing Plant Specimens.
A. Arranging and Preparing Specimens. After the specimens have been dug or cut they should be pressed as soon as possible (see V for information on field storage of fresh specimens). The care given a specimen in pressing will largely determine i ts future value. Specimens should be placed in a single fold of newsprint or other suitable absorbent lightweight paper. Plants too large to fit the 11" x 16" fold of paper may be bent into a "V", "N", or "M" figure. Bruise the stem before bending and it will be less apt to break. Specimens should not protrude from the fold of paper. Protruding parts will likely have to be removed when specimens are mounted. A specimen may be trimmed to reduce bulk and expose certain characters advantageously if suf ficient material (e.g., leaf petioles, branch bases, etc.) is left so that the pattern of branching, leaf arrangement, and other features are readily discernible. When pressing large plants are desirable make several sheets rather than a single sheet wit h a crumpled mass of material. Arrange specimens in such a way that some upper and some lower surfaces of the leaves are exposed. Spread flowers or inflorescences to show as many surfaces or views as possible. Section some flowers longitudinally and press flat to exhibit the inner parts and thereby reduce the need for dissection of the finished specimen.
Excessively bulky and fleshy parts such as stems and fruits may be split and both parts included. Fruits should be sectioned when possible in such a way that both transverse and longitudinal sections are included. Succulent plan ts (e.g., cacti) may be split and fleshy inner parts removed. Some prefer dipping them in boiling water, xylol or benzene before pressing. Salt may be applied to cut surfaces to hasten drying. Each sheet should bear a collector's number which refers to notes in the collector's field notebook. When using a series of sheets for parts of one specimen, number the paper with the collection and the number of parts (e.g., #429, sheet 1 of 3), duplicates should simply bear the collection number. Field notes are discussed below. Do not include more than one species in a single paper. Collect sufficient material to make a full sheet but avoid crowding or overlapping of specimens in the specimen paper. See Smith (1971) for an excellent illustrated account of specimen preparation.
B. Arranging the Press. Specimens (in the specimen paper) are placed between two driers in the press. A ventilator is often inserted before the next specimen paper and driers are added. For each specimen pressed a drier unit (2 driers with venti lator between them) is added to the press.The usual sequence is ventilator, drier, specimen in specimen paper, drier, ventilator, etc. As the successive specimens are added and the press built, every effort should be made to keep the press level for eve n distribution of pressure when the press straps or weights are applied. This will mean the use of alternate corners of the sheet for bulky roots or other parts. Sheets or pads of plastic sponges are very useful when placed over or around bulky specimens.
V. Field Storage of Specimens
Although it is desirable to press collections immediately, it may not always be practical. Delicate materials should be pressed as soon as possible and other specimens properly sorted. Vascula, plastic bags, or rubberized bags can be used for storage if specimens are first wrapped in moistened paper. Specimens may be kept in good shape without spoilage in the containers if they are kept moist and not packed too tightly. Supersaturation with water or drying out will spoil specimens. The specimen bags should be kept as cool as possible and a conscious effort should be made to park a specimen-loaded vehicle in the shade on field trips.
Upon return from the field, specimens in bags should be put into a coldroom until the plants are pressed. Although immediate pressing is again desirable, plants can be kept in this manner for several days.
Plastic gallon or half-gallon milk cartons or jugs make excellent water containers for field use. It is a good practice to wrap specimens collected at one locality in an uncut, numbered (with a wax pencil before paper is soaked), double sheet of newspaper so that one end is open and the other closed, bind with a rubber band, tag with a locality number which is entered in the field notebook, moisten and place upright in a bag, and then place the bag upright in the field vehicle. Moisten by sprinkling water over the open top of specimen bags as needed. If it is necessary to keep wet materials for long periods of time, as is necessary for collectors in tropical regions, several methods may be used:
|1. 2 parts commerical formaldehyde (40%):3 parts water.|
|2. 1 part formaldehyde:2 parts 70% alcohol.|
|3. 40-50% alcohol.|
|4. 1-2% aqueous solution of Oxyquinoline Sulfate.|
Specimens are dipped, sprayed or brushed with these solutions and enclosed in airtight packages. For additional details consult Fosberg and Sachet (1965) and Lawrence (1951) and Smith (1971).
VI. Drying Field Collections.
Plants should be placed in the press and the press closed and tightened. The faster the drying process the less difficulty with mold, mildew and loss of color. Plants should be sweated in the field press for 12-24 hours and the press opened. Any last ar rangement of the specimens must be made at this time and the wet driers hanged. For exceptional results driers should be changed at least three times during the first 48 hours. In many areas blotters may be dried in the sun (usually one hour is sufficie nt). If specimens are to be dried without artificial heat, blotters should be changed daily until specimens are dry. Automobile luggage carriers are excellent means of drying specimens provided ventilators with open ducts are used between the blotters.< BR> If artificial heat is used, there should be maximum airflow through the press. Never attempt to dry specimens in an oven. Use doublefaced corrugated cardboard or aluminum ventilators. A metal or wooden box with an open top which will accommodate a pre ss sideways (corrugations pointing up) and equipped with an electric heater with fan makes an excellent drying chamber. A collapsible drying frame (either a wooded box or metal frame with canvas skirt) may be used in the field and a camp stove ot lanter n used a heat source. Electric heating coils or light bulbs may also be used as heat sources but a fan should be installed either in or above the chamber. Special drying cabinets are sold but most lack sufficient ventilation for proper drying of speci mens.
VII. Data to Accompany Specimens.
A. Field Notes. As mentioned earlier every collector should keep a field book. This is not simply a road log. Each species collected at a given place and time should be given a collection number. The best system is to use a chronological one b eginning with number one and continuing from there. Avoid elaborate numbering systems with prefixes and cryptic notations or abbreviations. Do not use the same number for any other collection. All duplicates or replicates should bear the same collectio n or collector's number. Although some abbreviations may be useful and efficient in the field, these should be fully written out when permanent labels are made from the field notes. A specimen without field data (at least locality and date) is of no sci entific value.
Data to be recorded in the field notebook should include collector's number (for reference), exact locality, approximate altitude, nature of the habitat (type of soil, moisture conditions, slope exposure, light conditions), associated species, and other p ertinent information. With reference to the plant proper, record those features which will not be evident from the pressed specimen (height, branching, depth of root system, odor, etc.) and those features which may be lost in drying; e.g., flower color. Flower color may best be determined by using a color chart. The more complete the field notes, the more complete the permanent label can be and the greater the information content of the apecimen. B. Permanent Label. The permanent label is the label affixed to the mounting sheet with a specimen. Information included in addition to the name of the plant and authority (e.g., Claytonia caroliniana Michaux) must come from the collector's field notebook. Do not abbreviate or use symbols.
Specimens are now used throughout the world and symbols and abbreviations are often difficult to translate. Be specific in giving localities. If local names are used, give some reference to a city, major highway, or easily located reference point. Mini mum data for labels should include date, locality, county, state, collector and collection number. Labels, unless done by offset printing, should be typewritten using a carbon ribbon or written in longhand using india or other permanent ink. Paper shoul d be of high rag content--preferably 100%. See sample label ( 3 X 5) given below.
VIII. Identification of Collections
Materials should be identified using the appropriate manuals, floras and monographs (see chapter 30). If it is necessary to have materials identified or verified by a specialist, one of the duplicates is sent with a label to the specialist. Generally th e specialist will keep the specimen unless he has agreed to do otherwise. In the event that a duplicate specimen is identified by someone else, the collector should enter the plant name on the label followed by the name of the specialist and date that the duplicate was determined.
Once materials have been labeled and identified, they are ready to be mounted. (See Chapter 31).
- Davis, P. H., and V. H. Heywood. 1963. Principles of Angiosperm Taxonomy. Van Nostrand Company, Inc., New York.
- DeWolf, Gordon P., Jr. 1968. Notes on making an herbarium. Arnoldia 28: 69-111.
- Fogg, John M., Jr. 1940. Suggestions for collectors. Rhodora 42:145-157.
- Fosberg, F. R., and M. Sachet. 1965. Manual for tropical herbaria. Regnum Vegetabile 39. Utrecht.
- Franks, J. W. 1965. "A Guide to Herbarium Practice." Handbook for Museum Curators, Part E., Sec. 3, The Museums Association, London.
- Knudsen, J. W. 1972. Collecting and Preserving Plants and Animals. Harper and Row. New York.
- Lawrence, George H. M. 1951. Taxonomy of Vascular Plants. The MacMillan Company, New York.
- Pike, R. B. 1964. Plant pressing with plastic sponges. Rhodora 66: 172-176.
- Smith, C. E., Jr. 1971. "Preparing herbarium specimens of vascular plants." Agriculture Information Bulletin No. 348. U. S. Government Printing Office. Washington, D. C.