Significance of the Efficiency Index of Plant Growth. 89 
co-workers (7) who worked with a large number of plants, and 
have also analysed in full Gressler’s (4) data for Helianthus. 
This is now in the press (3). 
In the present note we wish to point out briefly what are the 
implications of the compound interest formula and to indicate how 
slightly these concord with the behaviour of such plants as have 
been so far investigated. 
In figures 1 and 2 graphs for Helianthus (Gressler), Zea Mais 
(Kreusler) and Sinapis alba (Hornberger) are presented, the rate 
of interest frorij week to week being plotted against time. 
