Grossenbacher — Radial Growth in Trees. 21 



growth is due to the environment the branches on the upper and 

 lower parts of the same tree must be dominated by different 

 factors. On measuring the cross sections of 100 large horizontal 

 branches of beech trees he found that of those arising on the 

 stems between eight and fifteen meters above ground 36% were 

 epinastic, 60% hyponastic and 4% of equal radius above and 

 below ; of those arising between fifteen and twenty meters above 

 ground 36% were epi — and 39% hyponastic and 24% had equal 

 radii above and below ; of those taken twenty to twenty-four me- 

 ters above ground 64% were epi — and 28% hyponastic, with only 

 7% having equal radii above and below. 



This opened up a phase of the problem, which is often left out 

 of consideration. It shows that the branches of some trees are 

 chiefly hyponastic on the lower part of trunks while they may 

 be predominately epinastic in the upper regions. From his tab- 

 ulated data the unmentioned and highly interesting fact may also 

 be gleaned that, of the 100 branches measured, 47 had the great- 

 est diameter in the horizontal plane and only 28 had the greatest 

 diameter, in the direction of gravity, while the other 25 wei*e 

 isodiametric. Although no special attention was directed to 

 these facts by Miiller he apparently was fully aware of them for 

 he concluded that gravity is not a factor in the distribution of 

 excentric radial growth, but that its distribution depends upon 

 illumination and the relative proximity to the channels of most 

 direct or greatest water and food conductance. Wiesner 36 who 

 has given this problem much attention, says that all inclined 

 stems of conifers are hyponastic or what he calls hypotrophic, 

 and that those of broad-leaved trees with little or no anisophylly 

 become first epinastic or epitrophic and eventually often become 

 greatly hyponastic, while species with marked anisophylly are 

 first hypotrophic and subsequently become epitrophic, and finally 

 hypotrophic again. He maintained that excentric or heterotro- 

 phic radial growth of a branch is due to its position both in rela- 

 tion to gravity and to the axis from which it arises. On the 

 other hand Gabnay 37 concludes that the difference in the specific 

 gravity of the elaborated food or of the cell content and the de- 

 gree of regenerative power possessed by the different classes of 



s " Wiesner, J. Ueber das ungleichseitige Dickenwachsthum des Holz- 

 korpers in Folge der Lage. Ber. Deut. Bot. Ges. 10:605-10. 1892. 



" Gabnay, P. Die Excentrizitat der Baume. Just's Bot. Jahresber 

 20:100. 1894. 



