Cuar. L. 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; but this occurs so much more 
* This whole subject has been 
ably discussed and explained by 
H. de Vries, ‘Arbeiten des Bot. 
Instituts in Wiirzburg,’ Heft iii. 
pp. 331, 336. Seealso Sachs (‘ Text- 
Book of Botany,’ English transla- 
tion, 1875, p. 770), who concludes 
“ that torsion is the result of growth 
continuing in the outer layers after 
it has ceased or begun to cease in 
the inner layers.” 
+ Professor Asa Gray has re- 
marked to me, in a letter, that in 
Thuja occidentalis the twisting of 
the bark is very conspicuous. The 
twist is generally to the right of 
the observer; but, in noticing 
about a hundred trunks, four or 
