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 OF TREE-TRUNKS AND THE DISTRIBUTION OF 
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 
00 1. c. 
61 1. c. 
