PLANT PHYSIOLOGY 385 



significance when applied to the process of culm-formation in 

 this grass. 



Mitscherlich (" Das Gesetz der Pflanzenwachstums," 

 Landw. Jahrb., liii, Heft 2, 1919, p. 167 ; " Ein Beitrag zum 

 Gesetz der Pflanzenwachstums," Fiihling's Landw. Ztg., Ixviii, 

 Heft 7-8, 1919, p. 130 ; and " Zum Gesetz der Pflanzenwach- 

 stums," — Fiihling's Landw. Ztg., Ixviii, Heft 21-22, 1919, p. 419) 

 has attempted to apply to plant-growth, as measured by 

 dry-weight increase, the following formula : 



log {yA - V >0 = log V~A - ex 



where n = a variable quantity indicating the probable number 

 of environmental factors, A = the maximum possible dry-weight 

 attainable by the plant in question, y == the dry-weight of the 

 plant at time x, the time x being expressed in vegetation periods 

 of arbitrary length. 



These various formulae to express the growth-rate of plants 

 are briefly considered and critically examined by O. Schiiepp 

 (" Ueber Form und Darstellung der Wachstumskurven," 

 Ber. d. deutsch. hot. Gesellsch., xxxviii, Heft 5, 1920, p. 193. 



Suggestions for the procedure to be adopted in a quantitative 

 study of the growth-rate of plants are put forward by West, 

 Briggs, and Kidd (" Methods and Significant Relations in the 

 Quantitative Analysis of Plant-growths," New PhyL, xix, 

 1920, p. 200). In this paper reference is made to previous 

 attempts to evaluate constants for plant-growth and certain 

 significant relations for a quantitative analysis of plant-growth 

 are given. In the first of a series of papers in which an attempt 

 is made to analyse the results of elaborate experiments carried 

 out in Germany on the growth of maize about fifty years ago 

 by Kreusler and his co-workers, Briggs, Kidd, and West (" A 

 Quantitative Analysis of Plant-growth. I," Ann. Appl. 

 Biol., vii, 1920, p. 103) have utilised two of the significant 

 relations referred to in the preceding paper ; namely, the 

 Relative Growth-rate curve, which is the weekly percentage 

 increase in dry-weight plotted against time, and the Leaf-area 

 Ratio curve, which is the leaf-area in cm.^ per gm. plotted 

 against time. It is shown that the growth-rate of maize varies 

 greatly in magnitude at different periods in its life-cycle in a 

 perfectly definite manner, and that the curve for leaf-area per 

 unit dry-weight throughout the season exhibits a correspond- 

 ence with the growth-rate curve, thus indicating that the 

 physiological basis for increased and decreased relative rate 

 of growth is a corresponding change in the assimilating area 

 per unit dry-weight. In the second paper of this series {Ann. 

 Appl. Biol., vii, 1920, p. 202) the authors have expressed the 



