RESPONSES TO ENVIRONMENT BY PLANTS IN THE VEGETATIVE PHASE 541 



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Light Level (daylight = lo) 



Figure 8. Interacting effects of (a) light intensity and (b) nutrient supply 

 on the net assimilation rate, leaf-area ratio and relative growth rate of Heli- 

 anthus annuiis. NPK: nitrogen, phosphorus, and potassium. C: control. 



rate and the leaf-area ratio. In other experiments, additions of N, P, and 

 K, alone and in combination, were investigated, but there were no 

 shade treatments. From these results it was concluded that the control 

 plants of Figure 8a were primarily deficient in P and K, while those of 

 Figure 8b were deficient in nitrogen also. 



Interrelationships between light and temperature 



It has already been emphasized that, in most of the previous at- 

 tempts to investigate the influence of seasonal changes in light and 

 temperature on growth and development, the experiments were not 

 designed with a view to eliminating ontogenetic drifts, variations in 

 mutual shading, and residual effects of the previous environmental con- 

 ditions. The approach of Goodall, in selecting plants with standard 

 morphological characteristics for each experiment, would be expected 

 to reduce the error. Further reductions should be accomplished by 

 selecting a stage early in the vegetative phase, when there is little self- 

 shading, and the residual environmental effects are likely to be mini- 

 mized if the intervening period from sowing is short. Pot experiments 



