Grossenbacher Radial Growth in Trees. 39 



only the first power of its horizontal diameter. He also con- 

 cluded that vertical stems may become excentric owing to one- 

 sided action of wind but that the effect on some trees might be 

 different on account of variations in the shape and the conse- 

 quent distribution of the weight of the top. The crooks in a 

 tree trunk are assumed also to be gradually eliminated by the 

 distribution of the radial growth in response to strain stimuli. 

 The same laws are thought to apply to the radial growth in roots 

 but because of the variation in the environing soil they are not 

 always so regularly effective. 



Yochting 74 cut the tips from some potted one-year-old savoy 

 plants and placed them with their pots in a horizontal position. 

 He attached weights to some near their decapitated tips and al- 

 lowed them to vegetate during some months. The vertical diam- 

 eter of the stems was markedly increased in the regions of great- 

 est strain while the stems of the check plants retained their 

 cylindrical forms. 



The far-reaching applicability of this wind-gravity hpyothe- 

 sis originating with Schwendener and elaborated by Metzger and 

 others, according to which tree-trunks and other stem structures 

 have a form required of a shaft of equal endurance throughout, 

 has recently been questioned by Jaccard. 75 He holds that the 

 hypothesis is untenable because measurements and calculations 

 made by him on a number of spruce trees resulted in a noncon- 

 formity of the hypothetical and actual forms of their trunks. 

 It was found that the portions of the trunks beginning with 5 

 m. above ground and extending to about 9 m. above ground were 

 practically of the form and dimensions required of such a shaft 

 but above and below that region the trunks were thicker than 

 required by the laws of mechanics. In one instance described 

 in detail, however, the trunk of a spruce practically conformed 

 to the required hypothetical shaft. 



Although much more frequent strong winds are said to occur 

 in western Switzerland the trees there were not found to differ 

 appreciably from those of eastern Switzerland where strong 

 winds are few. Jaccard maintained that during the growing sea- 

 son the wind is too spasmodic to be a factor in the distribution 



r * 1. c. 



75 Jaccard, P. Eine neue Auffassung uber die Ursachen des Dicken- 

 wachstums. Naturw. Zeit. Forst-u. Landwirts. 11:241-79. 1913. 



