26o 



H. POLSTER 



L S 



8- 



4- 



o 



2- 



20 



28 . 6 . 1957. 



Meteorological factor 



Assimi lotion 



North top 



North bottom 



South top 



South bottom 



~\ r 



6 



n r 



8 



— I 1 1 T" 



lO 12 



— 1 r- 



14 



— I r 



16 



20h 



Fig. 3. Assimilation in different crown regions at the borders of the stand. L= light 

 intensity in 1000 lux; S = water vapour pressure, mm mercury. 



were more exposed to light than the others, would show a stronger assimi- 

 lation than those of the north border. As a matter of fact, the following 

 figure proves the contrary for the dry period in summer (Fig. 3). The tree 

 of the northern border, better supphed with water, shows a much more 

 active assimilation in its top and also in its crown base than that of the 

 southern border. Moreover the difference between the crown tops wliich 

 are almost equally illuminated, is greater than that of the crown bases, 

 which means that compared to the water factor the hght factor plays only a 

 subordinate role in the intensity of photosynthesis of the poplars during dry 

 periods. 



