270 H. POLSTER 



diameter of the stand interior decreases quite obviously when compared 

 with the border trees: a fact which is well known from forest practice, 

 especially when there is a greater stand density. However, we are interested 

 above all in the correlation between water supply, assimilation efficiency 

 and growth capacity, which is to be seen most distinctly with the border 

 trees, and about that the reported facts informed us thoroughly. 



For a final observation I want to deal briefly with a problem which is of 

 the greatest importance for assimilation and transpiration physiologists. I 

 think that it emerges clearly from my results that the assimilation values 

 found for leaves or needles in any one crowm region, are never representa- 

 tive for the whole tree, and certainly are not so when the measurements 



Table 2 

 Stem height and diameter across the stand 



South North 



border 2nd row 3rd row 4th row 5th row border 



Stem diameter 5-2 



(cm in I m height) 

 Stem height (m) 5*09 



maximum deviation: 0-49 m stem height, 

 average deviation: ± 0-33 m stem height. 



have been made under extreme conditions of cHmate and site. The simple 

 transference of such values to the tree through multipHcation by the total 

 quantity of foHage is in any case faulty, if not false. Also the determination 

 of the difference of the carbon dioxide content in the air above the stand 

 and in the crown space, as performed by Huber and his collaborators, is 

 not reUable enough for a clear conception of the dry-matter production of 

 forest stands. If we wish to obtain an approximately true picture of the 

 dynamics of dry-matter production of trees and do not wish to renounce 

 determinations of assimilation as a physiological guide to the productivity 

 of adult trees, then- and this is how I estimate the present situation of 

 experimental forest ecology- there remains only a comparative determina- 

 tion of the assimilation efficiencies of the leaves in the different crown 

 regions. 



This is the course we are following. 



