a herbarium folder that becomes damp only when the river exceeds its banks, and dries again before noon.

Standard herbarium folio containing twelve mounted specimens, chiefly riparian weeds and two willow leaves. The folder remains dry under ordinary storage conditions. On nights when the adjacent river is recorded above flood stage, the folio shows uniform moisture within the closed covers, sufficient to soften the gummed strips and relax the specimens. No water staining is produced. The moisture is not confined to sheets bearing river plants and is present even when the folio is stored within a sealed tin chest. When flood conditions subside, the folder and contents return to their prior dryness by late morning, and the specimens resume their pressed profiles without mould.

The effect occurs in darkness and in lamplight. Heating the folio prevents condensation on its exterior but does not prevent the internal dampness. Substitution of blank paper for one sheet results in the blank sheet becoming damp to the same degree. When opened during an event, the dampness diminishes within minutes.