160 The Botanical Gazette. [March, 
other divisions of the elements occur in the same manner and 
in quick succession, the cells will all soon be inclined to the 
right, and in like manner if the walls incline to the left, the 
cells will incline to the left. The elements of the wood will 
be inclined as those of the cambium are inclined. 
In all of the specimens examined, if any twisting of the 
grain occurred during the first thirty years of the life of the 
tree, such twisting was found to be to the left. In about half 
of the specimens the twisting in this direction continued 
throughout the life of the tree. In the other half twisting 
did not make its appearance until well along in the life of the 
plant (then to the right) or changed from the left to the right 
in from thirty to one hundred twenty years. The inclination 
of the long axis of the elements from a radial plane varied 
from one to ninety degrees. In a little more than half of the 
specimens the angle of divergence increased regularly with 
the age of the tree.—L. S. CHENEY. 
The mechanics of curvature. 
The much vexed question of the curvature of organs in fe- 
sponse to various stimuli is again to the front, and a slight 
advance in the solution of the chief problem, 7. ¢., theit 
mediate cause of the curvature, may be claimed. Noll in @ 
recent contribution! meets the specific objections offered to 
his previous work? by Kohl® and Pfeffer. * 
The principal theories which have been successively at 
vanced in explanation of curvatures are chiefly as follows 
Sachs attributed it to the exaggerated growth in length 
the tissues on the side whose surface became convex in out 
line; DeVries to an induced heightened turgor of the convex 
side; Wortmann, in 1887, to the thickenings of the mer 
branes of the concave side and aggregation of protoplasm , 
the cells limited by them, and consequences in growth eae 
sion. In the large amount of critical work following this las 
contribution it was established that the migration of the ee 
toplasm and the thickening of the membranes on the concav’ 
side were attendant upon but bore no causal relation t0 - 
x 
2 
i . . 1894. darch 
“Energetik der Pflanzen. Leipsi ei : beitsleistunge? 
wachsende Pflanzen. Leipsic. 4 eg 1893.-Druck und Arbei 
