The Water Relations of Bracken: A Preliminary Study

In accordance with the pattern of experimentation used during the previous year in some exploratory field studies made in Aberdeen, a site was selected in a young mixed beech woodland with a moderately dense canopy in southern England (Kings Wood, Challock Forest, Kent; Grid Ref. TR025509). The site was located near the bottom of the gently sloping side of a small valley cut into the clay-with-flints plateau. The subsoil was a colluvium of chalk head and admixed clay-with-flints with a mean pH of 4-6, under a humus top stratum. Large clumps of Dryopteris filix-mas (L.) Schott were scattered in the dense stand of Pteridium. Measurements were made of leaf relative water content (relative turgidity; Weatherley 1950) by weighing entire pinnae, allowing them to come to full turgidity by immersing the base in a little water in a closed bottle under dim illumination and then reweighing before drying to a constant weight in an oven at 90? C. All samples were made in triplicate from the second branch from the base of the rachis, only the three or four lowest pinnae being used. Evaporation rate was determined by measuring the weight loss of