528 PLANT GROWTH AND PLANT COMMUNITIES 



In examining Kreusler's data for Z. mats, Briggs et al. adopted 

 linear measures in their estimates of unit leaf rate. They found that 

 after the eighth week from the early seedling stage the individual fig- 

 ures for the five varieties fluctuated widely, with a downward trend. 

 They decided, therefore, to employ only the results from the first eight 

 weeks, when the rate was rising, in an attempt to correlate variations 

 in the rate with changes in the environmental factors. After eliminating 

 doubtful records, they were left with only 15 to 20 figures from the sev- 

 eral years' experiments to correlate with the extensive meteorological 

 data Kreusler had collected. Employing simple correlations, without 

 any attempt to eliminate ontogenetic or time drifts, they correlated the 

 rate per week with the rainfall, the average maximum temperature, 

 and various parameters for light devised by Kreusler. On the basis of 

 these correlations, Briggs et al. concluded that above a level of one- 

 fifth of full sunlight light was no longer limiting the unit leaf rate. 

 However, since this correlation was 0.77, while those for total light or 

 hours of sunshine were 0.67 and 0.70, the evidence clearly was not very 

 conclusive. 



These authors also calculated the leaf-area ratio— that is to say, the 

 total leaf area divided by the plant weight— and observed that there 

 was a common trend for the ratio and the relative growth rate to rise 

 to a maximum about the fourth week, to fluctuate about this maximum 

 until the eighth week, and then to fall in the flowering and ripening 

 phases. Because of this similarity they came to the conclusion that in 

 maize "the unit leaf rate is roughly constant throughout the main parts 

 of the plant's life cycle." 



Lastly, Briggs et al. ( 1920-21 b, c) made an important contribution 

 to the quantitative analysis of growth. They pointed out that if the 

 changes in plant weight and leaf area are on an exponential basis, it 

 can be shown mathematically that the relative growth is the product 

 of the unit leaf rate and the leaf-area ratio, i.e.: 



1 dw 1 dw A 



W ~d^ "~ A "^ ^ \V 



In parenthesis, a quarter of a century elapsed before Williams 

 ( 1946 ) emphasized that unless the relationship between area ( A ) and 

 weight (W) over the given time interval (t2 — ti) is known, it is not 

 possible to integrate 



It 



dw di 

 t2 — ti I A dt 



