PLANT GROWTH AND THE AERIAL ENVIRONMENT

Abstract

S ummary If it cannot be assumed that the rate of increase of dry weight of a plant per unit leaf area (unit leaf rate or net assimilation rate) is constant, the computation of a mean value for this rate over a period between two harvests requires information or assumptions as to the relationship between dry weight ( W ) and leaf area (1). With sufficient information the problem can be solved graphically, but it is usual to assume either that W = a+bL or that W = a+bL 2 , where a and b are constants, leading to two well‐known formulae which suffice for many purposes. For more precise work, it is here shown that the solutions of a general case, W = a+bL n , where n is a third constant, are related to these formulae in a manner depending only upon n and upon p , the ratio of leaf areas at the first and second harvest. Various methods of computing the constants are described, their significance is discussed, and it is shown that for the young stages of certain plants n is close to I and the constant a is negligibly small. Later n increases, and the constant a becomes significant. Finally these methods are used to recompute the estimates of unit leaf rate given in Paper II of this series.