Camasa e cover. Aici fiind clar vorba de hartie, e "sheet".

The most delicate mounted specimens could be covered with a protective sheet of translucent paper, which must be rather strong and easy to fold. This paper can be used also to cover only parts of plants, such as fragile petals (Fig. 6).
http://www.funsci.com/fun3_en/herb/herb.htm
www.sbs.utexas.edu/jcabbott/courses/.../Collecting_Pressing...

To preserve their form and color, plants collected in the field are spread flat on sheets of newsprint and dried, usually in a plant press, between blotters or absorbent paper. The specimens, which are then mounted on sheets of stiff white paper, are labeled with all essential data, such as date and place found, description of the plant, altitude, and special habitat conditions. The sheet is then placed in a protective case. As a precaution against insect attack, the pressed plant is frozen or poisoned and the case disinfected.
http://en.wikipedia.org/wiki/Herbarium
http://www.answers.com/topic/herbarium
http://www.encyclopedia.com/topic/herbarium.aspx

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Note added at 1 oră (2010-01-12 11:16:21 GMT)
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Ar merge si "protective envelope/cover" dar asta doar in cayul unor ierbare de uz didactic. Exemplarele de plante din ierbarele stiintifice sunt depozitate in cutii de carton.

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Note added at 3 ore (2010-01-12 12:42:29 GMT)
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Pentru a le prezerva forma şi culoarea, plantele sunt puse între foi de hârtie absorbantă, şi apoi uscate şi presate, de obicei cu o presă de plante. Când sunt gata preparate, se prind de o foaie tare de hârtie albă, şi marcate cu datele esenţiale. Foaia este apoi pusă într-o cutie protectoare.
http://ro.wikipedia.org/wiki/Ierbar

Uite insa ceva f. interesant > informatii direct de la British National of Natural History :)

Location and storage
Almost all the collections are housed on upper floors in the Waterhouse building in South Kensington. Some lichen backlog material has been moved to the Museum outstation at Wandsworth. The majority of specimens are mounted on herbarium sheets and stored in standard wooden or metal cabinets. Other methods of specimen storage include:
• paper packets containing lichens and bryophytes.
• microscope slides of diatoms, microalgae, and pollen grains, housed in slide cabinets.
• spirit-preserved material of flowering plants, pteridophytes and algae, in metal cabinets.
• boxed collections of flowering plants, pteridophytes and crustose algae, stored in drawer-units.
• cardboard boxes containing backlogs of unincorporated collections.
http://www.nhm.ac.uk/resources-rx/files/life-earth-sciences-...
pg. 22

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Note added at 3 ore (2010-01-12 12:44:00 GMT)
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Museum