32 Wisconsin Academy of Sciences, Arts, and Letters. 



primary laterals and therefore exerts great pressure on the 

 cambium as Detlefsen 60 maintained. 



According to another group of investigators to be cited in the 

 discussion on the distribution of radial growth, excentric growth 

 is not due to an independent distribution of metabolized food and 

 the other factors commonly assumed to be effective. Both food 

 and growth are held to be distributed by the mechanical effects 

 of the environment in conjunction with the weight effects of the 

 structure in question or by the rate and path of the transpiration 

 current. 



THE GENERAL FORM OP TREE-TRUNKS AND THE DISTRIBUTION OP 

 RADIAL GROWTH. 



The distribution of radial growth on trees determines the form 

 of the stem and therefore its value as timber. Owing to the 

 economic importance of the shape of tree-trunks to the lumber- 

 ing industry foresters studied the distribution of radial growth 

 and its relation to the environment very extensively and have 

 collected many valuable data. Since the stem of a tree grown 

 in a fairly dense and uniform forest stand is relatively longer 

 and less tapering toward its upper end, free of branches and 

 therefore of more lumbering value than one grown in the open, 

 the differences in the environment of the two types have re- 

 ceived much attention. 



Nordlinger 61 noted that the yearly increase in thickness on the 

 branchless and branched parts of stems grown in a forest dif- 

 fered from each other. The annual distribution of radial growth 

 on the branch-bearing portion in a forest stand was found to be 

 similar to that on the entire trunk of a free-standing tree, which 

 bears branches nearly to its base. The thickness of the wood 

 rings in the branch-bearing part of stems was found to decrease 

 from the base upward. On the branchless portion of trunks in 

 dense forest stands the thickness of the recent rings was noticed 

 to have decreased from the branches downward although in some 

 cases the thickness of the new yearly growth remained practically 

 constant at the base of trunks. He thought that the presence 

 of elaborated food was not the only requisite for the occurrence 



"° 1. c. 

 01 1. c. 



