Notes on water relations ofPolytrichum communeHedw.

Water loss in the endohydric moss Polytrichum commune was found to be controlled by a complex series of leaf arrangement changes, and by changes in water potential deficit of the shoots. This contrasted with the water relations of the ectohydric moss Rhacomitrium lanuginosum in which there was apparently little control over loss. Water conduction in Polytrichum was predominantly internal under high evaporative flux, and external under moderate flux, but under many stress conditions both pathways would probably be necessary to maintain an optimum water balance.