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RESPONSES TO ENVIRONMENTAL FACTORS 

 BY PLANTS IN THE VEGETATIVE PHASE 



Geoffrey E, Blackman 



UNIVERSITY OF OXFORD ; 



You will recall that in the courtroom the' King of Hearts instructed the 

 White Rabbit to "begin at the beginning, go on to the end; then stop." 

 I was instructed to begin by discussing the genesis of the concepts of 

 growth analysis, and here history and filial duty dictate that I start 

 with my father. In 1919 V. H. Blackman, stimulated by the first in- 

 vestigation of one of his students, F. G. Gregory, on leaf expansion in 

 the cucumber, pointed out that the growth of an intact plant, as exem- 

 plified by the gain in weight, was a continuous process. He drew at- 

 tention to the fact that the changes in weight with time obeyed the 

 compound-interest law: that is to say, the gain at any time was pro- 

 portional to the amount of biological capital. On this basis, he criticized 

 the previous proposals put forward by Noll in 1906 that the best 

 measure of the rate of change in plant weight was the ratio that relates 

 the dry weights at two given time intervals ( "substanzquotient" ) . Such 

 a proposal erroneously implied that the relationship between time and 

 weight was linear; a far better measure of the rate of gain was the 

 difference between the logarithms of weight divided by the interval 

 between sampling occasions. 



Examining the field data on the growth of HeUanthiis anniius con- 

 tained in a doctoral thesis of Gressler, one of Noll's students, Blackman 

 demonstrated that for a considerable part of the growth cycle the cal- 

 culated rate was relatively constant. Blackman went on to point out 

 that "if the rate of assimilation per unit area of leaf surface and the 

 rate of respiration remain constant, and if the size of the leaf system 

 bears a constant relationship to the dry weight of the whole plant, 

 then the rate of production of new material as measured by the dry 



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