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 H.A. 35: 2031. 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.-R.B.