Chap. I. TWINING PLANTS. 9 



twisted.* Accordingly I allowed kidney-beans to run 

 up stretched string, and up smooth rods of iron and 

 glass, one-third of an inch in diameter, and they 

 became twisted only in that degree which follows as a 

 mechanical necessity from the spiral winding. The 

 stems, on the other hand, which had ascended ordinary 

 rough sticks were all more or less and generally much 

 twisted. The influence of the roughness of the support 

 in causing axial twisting was well seen in the stems 

 which had twined up the glass rods ; for these rods 

 were fixed into split sticks below, and were secured 

 above to cross sticks, and the stems in passing these 

 places became much twisted. As soon as the stems 

 which had ascended the iron rods reached the summit 

 and became free, they also became twisted ; and this 

 apparently occurred more quickly during windy than 

 during calm weather. Several other facts could be given, 

 showing that the axial twisting stands in some relation 

 to inequalities in the support, and likewise to the shoot 

 revolving freely without any support. Many plants, 

 which are not twiners, become in some degree twisted 

 round their own axes ; f but this occurs so much more 



* This whole subject has been it has ceased or begun to cease in 



ably discussed and explained by the inner layers." 



H. de Vries, 'Arbeiten des Bot. f Professor Asa Gray has re- 



Instituts in Wurzburg,' Heft iii. marked to me, in a letter, that in 



pp. 331,336. See also Sachs ('Text- Thuja occidentalis the twisting of 



Book of Botany,' English transla- the bark is very conspicuous. The 



tion, 1875, p. 770), who concludes twist is generally to the right of 



" that torsion is the result of growth the observer; but, in noticing 



continuing in the outer layers after about a hundred trunks, four ox 



