24 Wisconsin Academy of Sciences, Arts, and Letters. 
effects of the same thing. In case of branches, it was assumed 
that their weight increases the longitudinal bark tension above 
and reduces it underneath. Trees having one-sided tops were 
said to also be affected by the increase of bark tension on the side 
with fewer branches and a decrease on the top-heavy side, thus 
resulting in excentric growth of the stem with the greater radius 
on the side having more branches. A case was described in 
which a large horizontal branch had a sharp lateral bend on the 
concave side, which had resulted in a marked increase in radial 
growth with only a slight increase on the lower side. On such 
an assumption as this of Detlefsen it is conceivable that, after 
the excentricity in the upper angles of lateral roots has once be¬ 
come marked and a tree has attained some age, it may become 
more and more pronounced until a buttress-like structure results. 
However, he failed to mention epinastic branches. 
Kny 41 has also noted that bending roots of herbaceous plants 
and allowing them to grow in the bent position results in exces¬ 
sive growth of both xylem and cortex on the concave side. 
According to Mer 42 the two chief causes for excentric radial 
growth are those affecting the manufacture of organic food and 
those influencing cambial activity. The factors affecting the for¬ 
mer are the slope of the land, proximity to other trees, fertility 
of the soil, exposure, etc., while those influencing cambial activ¬ 
ity are thought, to be mechanical strains due to wind, gravity, 
traumatism, etc. Sloping ground is said to induce an increased 
growth on the hill and a reduced growth on tne valley side. 
Trunks were more commonly found excentric in thick than in 
thin forest stands and the excentricity was confined chiefly to 
the lower parts. When affected by the proximity of another 
tree the radius toward the influencing tree was shorter. Curva¬ 
ture was held to be the most frequent cause of excentric growth. 
Wounds were found to induce an excessive radial growth on the 
opposite side of the stem; and excentricity was found to be con¬ 
ducive to the occurrence of frost clefts. 
41 Kny, L. Ueber den Einfluss von Zug und Druck auf die Richtung 
der Scheidewande in sich theilenden Pflanzenzellen. Jahrb. Wiss. Bot. 
37:55-98. 1902. 
42 Mer, E. Recherches sur les causes d’ excentricite de la moelle dans 
le sapins. Rev. Eaux et Forets. Ser. 2:461-71; 523-30; 562-72. 1888. 
-3:19-27; 67-71; 119-30; 151-63; 197-217. 1889. 
