716 JOURNAL OF F0RE;STRY 



downward, and are also more heavily branched on the downward side, 

 one would expect a larger diameter development on the down side. 

 This is, however, not quite so ; in broadleaf trees, at least at the base, 

 the upper side radius is usually larger than the lower side, and this 

 eccentricity reaches considerably above breast height. 



The author explains this behavior as a reaction to geotropic stimulus. 

 For conifers, leaning or one-sidedly loaded, the stimulus of compres- 

 sion on the cambium accounts for the increased diameter growth on 

 the lower side ; also in part in broadleaf trees. Tensile forces have no 

 effect, since in that direction the strength of wood fiber is greatly in 

 excess of compression strength. Gravity is of influence on diameter 

 development of the lower stem parts only when it has been active on 

 the young shoots, as, for instance, when, due to light influence, the 

 plant had taken a leaning position. 



A series of experiments with 3 to 10 year-old trees, forcibly bent, 

 was used to show that bending woody shoots of broadleaf kinds always 

 is accompanied by increased diameter growth on the compression (con- 

 cave) side, the largest at the most severely bent part. 



A chapter is devoted to the character of the wood formed under 

 the stimulus of gravity and compression. 



The summary brings in twelve theses the results and conclusions. 

 Besides those we have already mentioned, we may add the following: 

 The ability to react to light and gravity is not possessed by all parts of 

 the tree alike. In the younger (higher) parts of stems the light stim- 

 ulus ; in the lower parts the gravity stimulus preponderates. The place 

 of reaction may be situated at a distance from the place where the 

 stimulus is felt, so that the basal parts may react by geotropic curva- 

 ture and eccentric diameter development to the gravity stimulus on the 

 growing end-shoots. 



The compression stimulus seems not to influence the summerwood 

 formation and histological character of the wood, but it increases the 

 volume increment. In ring-porous woods, however, the geotropic 

 wood shows broader porous area and relatively more summerwood, 

 and in drying shrinks more longitudinally than the wood of the under- 

 side. 



While classifying the forces at work, as is here done, advances our 

 knowledge of tree growth to some extent, we are really not yet in- 

 formed regarding the physiological processes active in the development 

 of these phenomena. 



The author suggests, however, that the curvature and other changes 



