It is important that dry specimens be prepared carefully so
that important morphological characters are displayed as
fully and completely as possible. Portions of the specimens
(fruiting structures or thallus sections) may be removed
and placed in a vial of preservative for microscopic
observation, which often is essential for identification.
The following procedure, with a bit of practice, should
produce good quality dried specimens.
1. Fixing the specimen:
The color of most specimens is best preserved by "fixing"
the specimens in 3-5% buffered
Formalin seawater (see Preserving specimens in liquid preservatives) away from direct sunlight (overnight fixation is adequate but algae may remain for longer periods of time without damage in this preservative if kept away from light, which causes bleaching). Deterioration may commence upon collection, so it is advantageous to have Formalin handy immediately following collection.
The staff of the U.S. National Herbarium prefers to sort the collection by taxa, while still in the field. The specimens are then preserved in separate plastic whirl-pac bags into which waterproof labels have been inserted. All of the specimens from a station are
placed in a large labeled plastic bag which is then placed in a light-proof shipping container (liqua-pac).
2. Preparing the specimens:
- Fleshy specimens.
- Having been properly fixed, fleshy specimens should be
rinsed free of any sand or debris. (Tap water may be used
for this.) Remove any artifacts (shells, animals) which are
not part of the specimen -- although records of their
presence should be made for ecological reference. If the
holdfast is too thick and resistant to be pressed, either
split it to remove portions, thereby facilitating pressing,
or remove the holdfast and dry it separately (properly
tagged for reference to the original specimen).
- Calcareous specimens.
After first fixing the specimens in 3-5 % Formalin, select portions to be liquid preserved in a vial. Soak for several days in a solution of about 40% glycerin in 3% buffered
Formalin seawater. Dry and place in small boxes without pressing or, where appropriate, glue carefully to herbarium paper.
Additional information may be found at: An Introduction to Nongeniculate Coralline Algae.
This server is maintained by Derek Keats at the University of the
Western Cape, South Africa.
NOTE: Some researchers
prefer that glycerin not be used, as it may harm the reproductive
structures inside the conceptacles.
3. Pressing the specimen:
Prior to pressing the specimen, a number or note should be
written on the lower right hand corner of the herbarium sheet (unbuffered long-fiber 100% rag mounting paper 11 1/2" x 16 1/2" - 70M; White-Caliper.015)
. This will aid in identifying specimens and allow
for affixing the proper herbarium label after pressing.
Also keep in mind the layout of the herbarium sheet when
placing specimens on the sheet with regard to the label
location (lower right corner) and herbarium stamp (usually
upper right corner).
- The larger coarser forms may be placed directly on
herbarium paper. However, delicate forms must be placed
on the paper while it is submerged in a tray or pan of
adequate size containing water (it may be tap water if
specimens have been fixed), which will allow for spreading
- Place specimen (in water) over paper, and using forceps,
a pointed instrument, or a small, soft paint brush for
more delicate forms, pull out and separate branches, and
spread the specimen to reveal branching patterns and small
structures. If necessary, trim away (and note that this was
done) an appropriate amount of the specimen where excess
material obscures structures.
- Remove the paper very carefully from the tray, at an
angle so that water flows will tend to spread the branches
as the paper is being lifted. A squirt bottle of water may
be used at this point to further spread branches. Place the
paper containing the specimen(s) on a blotter. Then place a piece
of muslin, cheesecloth, a cloth "diaper" or crumpled waxed
paper over the specimen, and add another blotter on top.
- Place the blotter and specimen sandwich between standard
plant press ventilators (corrugated cardboard or aluminum).
- Continue adding specimens to the plant press so that each
specimen is covered with non-sticking material and between a layer of
blotters, enclosed by a layer of ventilators. Finally,
firmly tighten the straps of the plant press.
- Moderately warm artificial heat should be applied from
below the press as it is placed on its side so that warm
dry air passes upward through the corrugations of the
ventilators. Alternately, the plant press may be placed in
a fume hood so that the sash closes on the press, allowing
air to be drawn through the corrugations.
Heaters may be devised which include a rack to hold the
press and a heating source, such as light bulbs, a heating coil
or a hot plate. Note that warm air is all that is required.
Too much heat will cause the algae to darken and become
brittle. Check specimens at least every 24 hours removing
any that are dry; wet blotters and "diapers" should be
changed and the straps of the plant press retigntened.
If a heat source is not available, blotters and diapers must
be removed daily and replaced with dry ones.
Drying may require many days by this method, so a heat source
should be used if at all possible.
- Remove press from heat source and allow to cool with the
straps tightened before opening. Specimens may curl if exposed to a humid
atmosphere before cooling, in which case they must be wetted
4. Gluing the dried specimen:
Many specimens will remain attached to the herbarium sheet
following drying due to the presence in the algal walls and
intercellular spaces of colloidal "glues". The coarser,
non-gelatinous forms (e.g. some Phaeophyta) may not remain
attached after drying and may require "glue".
Any good clear-drying glue may be adequate, such as white glue
or a white PVA resin. However due to problems with white glue
becoming soft / sticky again (under humid conditions), the
U.S. National Herbarium prefers to use
"tin" paste applied in spots, to the underside of the specimen.
Gummed linen herbarium tapes may also be used to
"strap" the specimen(s) to the sheet.
5. Applying specimen label:
Using good quality (100% rag acid-free) herbarium label paper, complete the label and affix by means of a clear-drying cement (tin paste), to the lower right-hand corner of
the sheet. AVOID gummed labels on poor quality paper.
herbarium sheet should include a
label, and may also have museum and barcode numbers, as well as annotation notes written directly on the sheet or on spereate labels.