A diffusive resistance porometer for field use. 1. Construction.
Details are given of the construction of a diffusion porometer for measuring stomatal resistances of leaf surfaces, based on principles described in F.C.A. 18: 2163. Water vapour from inside the leaf diffuses into an initially dry cup clipped on to it; after calibration, the surface resistance is estimated from the rate of increase of humidity in the cup. The humidity-sensing element is sulphonated polystyrene. [See also abs. 2202]-R.B.