PHOTOSYNTHESIS AND GROWTH OF POPLAR TREES 261 



10. 7. 57. 



L S 

 -20 



40 



20 



10 



10- 



8- 



* 6- 



O 

 U 

 01 4 



E 



2- 



Meteorological factor 



Assimilation 



1st tree 



2nd tree 



3rd tree 



4th tree 



—\ — 



leh 



Fig. 4. Assimilation in crown tops across the stand. L and S as in Fig. 3. 



If one considers not only the border trees but also the trees standing 

 between the northern and southern border (Fig. 4), one will find a correla- 

 tive ascent of the assimilation intensity corresponding to the soil moisture 

 from the southern border across the middle of the stand to the northern 

 border. As the curves show, tree No. 2, standing very close to the southern 

 border, is still completely under the influence of the southern border's 

 dryness; tree No. 3 in the middle of the stand, reaches almost the assimila- 

 tion eflficiency of the northern border tree in the morning, but at midday it 



