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 wind-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 

 trunks 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 



™ Metzger, A. Studien iiber den Aufbau der Waldbaume und 

 Bestande nach statischen Gesetzen. Mundener Forstl. Hefte. 5:61-74. 

 1894. Mundener Forstl. Hefte. 6:94-119. 1894. 



