22 Wisconsin Academy of Sciences, Arts, and Letters. 
trees are the factors determining whether excentric growth shall 
be epi- or hypotrophic. The specific gravity of the elaborated 
food of conifers was found appreciably greater than that of 
broad-leaved trees. The regenerative power of a tree is said to 
be inversely proportional to the specific gravity of its elaborated 
food and it is held that the greater the regenerative power of a 
tree the more epitrophic it is, while the lower its regenerative 
power the more hypotrophic. 
From his observations on the influence of the environment on 
radial growth Kny 38 concludes that the exeentricity of horizon¬ 
tal branches is not only a reaction to gravity but that it is also 
influenced by the relative illumination, transverse bark tension, 
etc., as well as by some unknown factors. In some plants the 
greatest thickness of one wood ring is on the lower side of a 
branch while subsequent rings may be thicker above. The 
branches of most of the broad-leaved woody plants were found 
to have the upper half of the wood cylinder of greater thickness 
than the lower, but quite a number of exceptions were also noted, 
e. g. Tilia, Cydonia, Fraxinus, Gleditschia, Corylus and Alnus. 
The branches of conifers on the other hand are thickened in ex¬ 
cess chiefly on the lower side. In general it was found that one 
type of exeentricity is characteristic of certain natural groups 
of plants, but isolated exceptions were often noted indicating 
that gravity plays a minor part in the distribution of radial 
growth. The upper side of branches is subject to greater varia¬ 
tions of light, temperature and moisture than the lower and it 
was thought that perhaps bark tension might be less on the up¬ 
per side owing to the greater distension of the bark on that side 
by the variations of the temperature; yet since the results may 
be just opposite in neighboring trees of different groups having 
the same environment no conclusions were thought admissible. 
It was observed that, owing to the fact that all leaves and buds 
attached to the under side of a lateral branch develop and grow 
most strongly, the axis is usually thicker on the lower side dur¬ 
ing the first year, while in subsequent years the branches on the 
upper side of a horizontal branch grow more rapidly than those 
on the lower and thus result in changing hyponastic to epinastic 
branches. A case is cited where the stems of Ficus stipulata 
38 Kny, L. Ueber das Dickenwachsthum des Holzkoerpers in seiner 
Abhaengigkeit von aeussern Einfiuesen. pp. 136. Berlin 1882. 
