96 Significance of the Efficiency Index of Plant Growth. 
physiological constant and as an index of efficiency is not really 
constant at all in the plants which have been investigated. This 
index is of no value in comparing the efficiency of different plants, 
except over strictly comparable times and phases of development, 
so that the application of the formula by Brenchley in comparing 
plants of different degrees of maturity is not valid. 
Botany School, Cambridge. February , 1920. 
LITERATURE CITED. 
1. Blackman, V. H. The Compound Interest Law and Plant Growth. Ann. 
of Bot., XXXIII, 1919, p. 353. 
2. Brenchley, W. E. Some Factors in Plant Competition. Ann. of Appl. 
Biol., VI, 1919, p. 142. 
3. Briggs, G. E., Kidd, F. and West C. Quantitative Analysis of Plant 
Growth. Ann. of Appl. Biol. VII, 1920. (In the 
Press). 
4. Gressler, P. t T ber die Su,bstanzquotienten von Helianthus annum. Inaug. 
Diss., Bonn, 1907, pp. 1—25, tables I —V. 
5. Hornberger, R. Untersuchungen iiber Gehalt und Zunahmen von Sinapis 
alba an Trockensubstanz und chemischen Bestand- 
theilen in 7 —tagigen Vegetationsperioden. Landw. 
Versuchs—St., XXXI, 1885. p. 415. 
6 . Kidd, F. and West, C. Physiological Pre-Determination. The Influence 
of the Physiological Condition of the Seed upon the 
Course of Subsequent Growth and upon the Yield. 
IV. Review of Literature. Chapter III. Ann. of 
Appl. Biol., V, 1919, p. 220. 
7. Kreusler, U. et al. Beobachtungen iiber das Wachsthum der Maispflanze. 
Landw. Jahrb., 1877-9 
