F. KiDD AND C. West 



231 



( J ) the initial 'capital,'' and (2) the " rate of interest^"' The first of these 

 factors has a pre-determining effect upon the development of the plant 

 and cannot be influenced by subsequent environmental conditions, but 

 the second factor would naturally be under the influence to some extent 

 of the environmental conditions obtaining during the main growth 

 period of the plant. 



Curve a in Fig. 2 shows the change occurring from week to week in 

 the "rate of interest" of the growth of normal plants. In this case the 

 " rate of interest " or, in other words, the "efficiency " of the plant is at its 

 maximum during the second week of growth and subsequently gradually 

 falls throughout the course of later development^. 



T 



"76^ 

 WEEK 



Fig. 2. Change in the percentage increase in dry weight from week to week (i.e. " rate 

 of interest") in the case of a, normal plants of Helianthus annuus Bismarckianus ; 

 b, plants from which one cotyledon and one foliage leaf had been removed; c, plants 

 from which both cotyledons had been removed. 



^ The German authors used the expression "Substanzquotient," which is the dry 

 weight of the plant at time n divided by the dry weight of the plant at the time n -1. 

 The unit of time taken is arbitrary and is one week. It seems to us more suitable to use 

 the expression "rate of interest." The "rate of interest" = 100 (Substanzquotient - 1). 



* In the case of the data obtained by Gericke the question which immediately pre- 

 sents itself is how far the fall in the "rate of interest" curve is due to inherent causes 

 and how far it is due to the hmiting factors of the environment, e.g. hght. Gericke's data 

 allow one to rule out temperature, but the author himself suggests the possibihty of light 

 as the hmiting factor. The seeds were sown during the end of May and the beginning ot 

 June. . 



