摘要: DR. LEVITT1 directly compares a resistance for flow of liquid water with one gaseous diffusion vapour. A comparison the resistances in plant tissues those phase is, however, only possible even as an approximation if both are expressed terms same fluid. If this is made vapour we can specify, each part system that considered separately, equivalent air path ; tube unit cross-sectional area such length that, potential difference (ΔP) maintained between its two ends, it would allow net observed to pass through steady state.