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 weke 
isodiametric. Although no special attention was directed to 
these facts by Muller 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 
becouie 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 
38 Wiesner, J. Ueber das ungleichseitige Dickenwachsthnm des Holz- 
korpers in Polge der Lage. Ber. Deut. Bot. Ges. 10:605-10. 1892. 
87 Gabnay, F. Die Excentrizitat der Baume. Just’s Bot. Jahresber. 
20:100. 1894. 
