j-j Wisconsin Academy of Sciences, Arts, and Letters. 



trees are the factors determining whether excentric growth shall 

 be ,.,,; , , i.vpotrophic. The specific gravity of the elaborated 

 food i conifers was found appreciably greater than that of 

 broad-leaved trees. The regenerative power of a tree is said to 

 I,,. inv< rsely 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 

 pmvrr the more hypotrophic. 



From his observations on the influence of the environment, on 

 radial jrrowth Kny 38 concludes that the excentricity 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 

 nches of most of the broad-leaved woody plants were found 

 to have the upper half of the wood cylinder of greater thickness 

 Ilian the lower, but quite a number of exceptions were also noted, 

 e. g. Tilia, Cydonia, Fraxinus, Gleditsehia, Corylus and Alnus. 

 The branches of conifers on the other hand are thickened in ex- 

 ci ss ri>':'fiy on the lower side. In general it was found that one 

 type of excentricity 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 

 just opposite in neighboring trees of different groups having 

 tho 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 



18 Kny, L. Ueber das Dickenwachsthum des Holzkoerpers in seiner 

 Abhaengigkeit von aeussern Einfluesen. pp. 136. Berlin 1882. 



