554 PLANT GROWTH AND PLANT COMMUNITIES 



no corresponding increases in internode length; the influence is entirely 

 inhibitory. 



These results serve to illustrate that the leaf area and internode 

 length can be modified in a specific manner by diflFerent compounds, 

 but it must be stressed that all the investigations were carried out at 

 25° C. and at light intensities of 300 and 600 foot-candles. It has yet 

 to be demonstrated to what extent the observed responses will vary 

 under other combinations of light and temperature. 



Within the compass of my allotted time it is an inevitable con- 

 sequence that any appraisal of four decades of research must be selec- 

 tive, and I am fully conscious of many omissions. I have now given my 

 evidence and must stop, but I end in a state similar to that of the Mad 

 Hatter after the King said, "Give your evidence and don't be nervous 

 or I'll have you executed on the spot." My anxiety arises from the fact 

 that in this survey of the analytical interpretation of plant responses to 

 environmental factors it seems ungracious that I have made no refer- 

 ence to American workers. This omission is not perverse but is due to 

 my inability to trace a body of papers where the techniques of growth 

 analysis have been fully exploited. This divergence of interest I have 

 discussed on previous visits to the United States, and the opinion has 

 been expressed that the concepts are crude and yield but meager in- 

 formation concerning the basic physiological processes that determine 

 the reactions of plants to the environmental factors. My reply has been 

 that it is essential to match what is learned in the laboratory with an 

 equal and precise knowledge of the reactions of the plant as a whole 

 for a wide range of species and conditions. My hope is that this paper 

 is persuasive enough to support my contention that there is a con- 

 tinuum between research involving the cold room and centrifuge and 

 field experimentation seeking to assess plant performance. 



References 



Ashby, E., and Oxley, T. A., 1935. "The Interaction of Factors in the Growth of 

 Lemna minor, IV: An Analysis of the Influence of Light and Temperature on 

 the Assimilation Rate and the Rate of Frond Production," Ann. Bot. 49, 309. 



Black, J. N., 1955. "The Interaction of Light and Temperature in Determining 

 the Growth Rate of Subterranean Clover ( TrifoJium subterraneum ) ," Atistr. 

 J. Biol. Sci. 8, 330. 



Blackman, G. E., 1957. "Influence of Light and Temperature on the Growth 

 of Leaves," in Milthorpe, F. L., ed.. The Growth of Leaves (London, Butter- 

 worth Scientific Publications). 



Blackman, G. E., and Black, J. N., 1959. "Physiological and Ecological Studies in 

 the Analysis of Plant Environment, XI: A Further Assessment of the Influence 

 of Shading on the Growth of Different Species in the Vegetative Phase," 

 Ann. Bot. N.S. 23, 51. 



