Grossenbacher — Radial Growth in Trees. 27 



son. The excessive growth at the curve and the accompanying 

 "red- wood" was found to have developed on the under or con- 

 vex side of the curve. This was assumed to indicate that grav- 

 ity has more influence in the production of "red-wood" than 

 longitudinal compression. 



Rubner 48 has given us some interesting observations on ex- 

 centrix as well as of more irregularly distributed radial growth 

 of trees. He called attention to the fluted or furrowed trunks 

 and buttressed trunk-bases so characteristic of certain species. 

 He attributed the ridges to excessive and the valleys to subnor- 

 mal radial growth. In Carpinus the deep, wide grooves in the 

 stem were found to occur at places where several compound 

 medullary rays are grouped together, while lesser depressions 

 or channels occurred along each individual compound ray, but 

 these lesser grooves were practically compensated for by the 

 greater phloem production so that the outer surface of the bark 

 did not show them. In portions of trunks represented by the 

 ridges the rays were small and it was assumed by Rubner that 

 the distribution of the large and small rays influences the rel- 

 ative amounts of radial growth of the ridges and valleys in the 

 wood cylinder. While Nordlinger 47 assumed that the valleys 

 are due to an excessive bark pressure along the large rays owing 

 to the development of stone cells or abnormally long phloem-ray' 

 cells in the bark at such places. He notes the absence of marked 

 valleys and grooves in oaks devoid of broad rays, and that on 

 very large, old trees the outer rings often have the valleys be- 

 tween the large rays while the ridges occur along the rays. The 

 armpit-like depressions below some branches, according to Rub- 

 ner, occur under branches whose leaves elaborate only enough 

 food for their own use thereby leaving the region just below the 

 branch bases insufficiently supplied, owing to the deflection the 

 branch-bases cause in the downward current of food in the trunk. 

 These depressions are said to be chiefly confined to epinastic 

 species. In the valleys Rubner found the wood to consist main- 

 ly of thick-walled fibers and the radial arrangement of the cells 

 was perfect, apparently because the valley-wood is devoid of ves- 

 sels. The large "false rays" present in the valleys of Carpinus 



40 Rubner, K. Das Hungern des Cambiums und das Aussetzen der 

 Jahrringe. Naturw. Zelt. Forst-u. Landw. 8:212-62 1910. 



"Nordlinger, H. Wirkung des Rindendruckes auf die Form der 

 Holzringe. Centralbl. Gesam. Forstwesen. 6:407-13. 1880. 



