:M Wisconsin Academy of Sciences, Arts, and Letters. 



efiYets of the same thing. In case of branches, it was assumed 



that their weight increases the longitudinal bark tension above 



and i-i 'diiccs 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" 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- 

 ^ 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. 

 '(rands 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. 



?^ y '-P' - Ueber den Einfluss von Zug und Druck auf die Richtune 

 37 5^8 iloT 6 ^ SiCh theilenden PflaDZenZe llen ' Jahrb wil Bot g 



Ss E ' R?v eC erCheS * r I 68 CaUS6S d ' excen tricite de la mobile dans 



^r 8 ' Ser " 2:461 -?l; 523-30; 562-72. 1888. 

 9-30; 151-63; 197-217. 1889. 



