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TEXTBOOK OF PLANT PHYSIOLOGY 



continuously in accord with the diurnal and annual fluctuation of 

 solar radiation. One of the first attempts to ascertain the relative 



Fig. 14. — Development of the shade plant Teucrium scorodonia (above) and of the 



heliophilous plant Amaranthus retroflexus (below) under different light conditions. 



The figures under the drawings show what part of the total daylight was obtained 



by the plants during their development (redrawn from Combes). 



minimal amount of light at which the plant is able to develop was 

 made by Wiesner. He determined the intensity of light during 

 the noon hours in the most shaded habitats where certain 



