36 Wisconsin Academy of Sciences, Arts, and Letters. 
branches like in trunks wind effects predominate over the weight 
of the structures themselves as formative stimuli. Branches in 
positions intermediate between these two extremes are said to be 
correspondingly influenced by the two factors. Since conifers 
of various sizes were found to conform very closely to the hy¬ 
pothetical requirements, Metzger thought it logical to assume 
that wind and the weight of the supported structures themselves 
are the factors instrumental in shaping tree-trunks or distribut¬ 
ing radial growth on them. When the lower branches of a free¬ 
standing tree were removed, it was found that the annual 
growths on the lower portion of the trunk were reduced in cross- 
sectional area in very nearly the proportion required by the 
hypothetical considerations of the upward movement of the 
point of greatest stress. When a free-standing tree is encom¬ 
passed by young trees radial growth of its trunk decreases from 
above downward as required by this hypothesis. When forest 
trees are left free-standing by the removal of surrounding trees 
radial growth is found to increase on their trunks from above 
downward and to decrease below normal on the upper part of 
the stems. In conformity also with the above hypothetical re¬ 
quirements the tall or over-topping trees in a forest of mixed 
sizes undergo most radial growth on the lower parts of the trunks 
while the overtopped trees grow more on the upper part of 
trunks. 
Although these conclusions were based on data, which were 
obtained from spruce, Metzger 70 thinks them applicable to the 
distribution of radial growth of trees in general. According to 
him the wind, acting as a stimulus through its mechanical effects 
upon trees, also regulates in a general way, the distribution of 
the elaborated food as well as that of radial and elongation 
growth in accordance with the relation of the form of the top, 
etc. to vdnd-exposure. It is said that during the first and sec¬ 
ond year after the thinning of a forest most of the available food 
is used up in increasing radial growth on the lower part of the 
tranks so as to increase the wind resisting power of the suddenly 
exposed trees, but afterwards elongation growth proceeds rap¬ 
idly. In some cases of this kind it is held that the top may be 
70 Metzger, A. Studien iiber den Aufbau der Waldbaume und 
Bestande nach statischen Gesetzen. Miindener Forstl. Hefte. 5:61-74. 
1894. Miindener Forstl. Hefte. 6:94-119. 1894. 
