204 
C. West , G. E. Briggs , and F. Kidd. 
The Belative Growth Bate , R, is the weekly percentage rate at 
which the dry-weight increases. It may be assumed for purposes 
of calculation that the increase from week to week takes place 
exponentially, R being the exponent, or that it takes place linearly. 
Both are approximations. As to the relative merits of the two 
different methods the reader is referred to (4). If R be the 
dW RW 
Belative Growth Bate and W the dry weight then “^“= r 'J()o • This 
formula expresses the relation between R and W assuming the 
increase takes place exponentially and when integrated the equation 
becomes log e W 2 —logeW^y^, where W 2 is the dry-weight at the 
end of the week, Wj the dry-weight at the beginning of the week 
and e the base of the natural logarithms. If it is assumed that 
R W 2 —W, 
the increase is linear jqq =—yy -* 
By Leaf Area Batio, A, is meant the ratio of leaf-area to dry- 
L + L 2 
weight, that is —. For simplicity 2 is used when making 
w w; 
calculations on the linear basis, Lj being the leaf-area at the 
beginning of the week and L 2 at the end of the week. 
By Unit Leaf Bate, E, is meant the weekly rate of increase in 
dW 
dry-weight per Unit Leaf Area. 1 Then —-jj- =EL, and if the 
exponential basis be adopted for both leaf-area and dry-weight 
W _W 
increase, then E=(log e L 2 —log e L,) - T ——- 1 . On the linear basis 
l . 2 
W-W, 
for leaf-area E == L,-|-L g , that is, the weekly increase in dry 
2 
weight divided by the Average Leaf Area. 
Belative Leaf Growth Bate , R L , is analogous to Relative 
Growth Rate and —=log e L 2 —log e L lt or —-2--1 according to 
1UU L | 
whether the calculations assume an increase on the exponential or 
on the linear basis. 
An inspection of the above definitions and formulae will show 
that whichever formal conception as to the mode of increase of 
dry-weight and leaf-area be adopted the Relative Growth Rate is 
merely the product of the Leaf Area Ratio and the Unit Leaf 
1 Cf. Weber’s “ Specifische Assimilationsenergie ” (15). 
