Quantitative Analysis of Plant Growth. 205 
Rate multiplied by 100. This will be made clear by the following. 
dW dW 
100 • ^ 
On the exponential basis R=-——, A—^ and E=-j— and 
hence R=100A.E. On the simple interest basis it will be seen 
that the same relationship holds. None of the above formulae 
involve the assumption that R, Rl, A or E are constant throughout 
the life-cycle. 
An examination of data shows that in the early part of the 
plant growth the increment of dry-weight and of leaf-area is more 
or less exponential, whilst later it approaches to being linear. Thus 
in order that the calculated rates may approximate more closely 
to accuracy, especially in the case of the Unit Leaf Rate, the 
exponential basis should be adopted in the early period whilst in 
the later period it makes little difference in the calculated rate 
which basis of calculation be adopted. The importance of 
obtaining values for Unit Leaf Rate which approach closely to 
accuracy is that these values may be compared with values of 
assimilation determined by gasometric and half-leaf methods. 
Our reason for adopting Unit Leaf Rate as a significant 
relation in the analysis of plant growth is that we have at our 
disposal a certain amount of definite knowledge with regard to the 
effect of environmental factors upon assimilation. By making the 
necessary allowances for variations in environmental factors we 
can determine to what extent assimilation controls growth and to 
what extent it is controlled by growth. 
Another problem which can be attacked by the above method 
is as to how far differences in Relative Growth Rate of different 
plants are due to differences in Unit Leaf Rate and how far to 
differences in Leaf Area Ratio. This problem is now under 
experimental investigation by the authors. 
In the case of maize the ratio of productive to total weight is 
not constant but the Relative Growth Rate and Leaf Area Ratio 
undergo similar and simultaneous variations, thus suggesting that 
Unit Leaf Rate is roughly constant throughout the main parts of 
the plant’s life-cycle, and that, considering the growth of a plant 
as analogous to money accumulating interest, the leaf-area is a 
better measure of capital than is the dry-weight. 
The above suggestions are to be considered simply as 
proposals for formal methods of assembling secondary data on 
what appear to be the most profitable lines as a result of the 
closest inspection possible at present. It is to be emphasised that 
