G. E. Briggs, F. Kidd, and C. West 221 



Leaf Rate calculated for the later phases of the life-cycle have been 

 attributed mainly to sampling errors. 



Correlations between Unit Leaf Rate and various environmental 

 factors have been determined. 



The general evidence is that the Unit Leaf Rate is correlated more 

 closely with temperature than with any of the other environmental 

 factors. 



By allowing for respiration on the basis of our own experimental 

 results values for the real assimilation were arrived at. These also show 

 a closer correlation with temperature than with light. 



The values for assimilation determined from the Unit Leaf Rate are 

 of a lower order than those determined by the "half-leaf" method, but 

 much higher than those determined by the "gasometric" method. 



Finally, the authors wish to express their indebtedness to Dr F. F. 

 Blackman for his stimulating criticism and help in this and in the previous 

 chapter. 



(To be continued.) 



APPENDIX. 



The definitions and inter-relation of the terms used by the present 

 writers in their analysis of plant growth are as follows (22): 



The relative groivth-rale, 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, -— being the 



exponent, or that it takes place linearly. Both are approximations. If 



dW RW 



W be the dry-weight -7- = -r—r . This formula expresses the relation 

 J (II 100 . 



between R and W assuming the increase takes place exponentially and 



r> 



when integrated the equation becomes log e W 2 — log,, W x = — A , where 



W 2 is the dry-weight at the end of the week, W x at the beginning of the 



week and e the base of the natural logarithms. If it is assumed that the 



. .. R W 2 - ]\\ 



increase is linear 



100 w ! + w, 



2 

 Leaf-area ratio, A, is the ratio of leaf-area to dry-weight, that is 



^ . For simplicity —± — ~ is used when making calculations on the 

 Ann. Biol, vn 15 



