210 
Tf, after 12 hours, as soon as a distinct increase in curvature 
is perceptible, the hook-tendrils, either whole, or in the form of 
a median longitudinal slice, are placed in plasmolytic solutions, 
no perceptible straightening takes place, nor is the curvature 
affected, if tendrils, which have been 12 hours or 1 day in 
contact, are dropped into absolute alcohol, and then, after a 
time, placed in water. It follows therefore, that, if the curvature 
is produced by a difference of turgidity between the two sides, 
the difference is but slight, and that the curvature produced is 
rapidly followed up, and rendered permanent, by growth. It is 
not, however, probable, that a slight difference of turgidity could 
directly cause the secondary curvature of so stiff an organ, as 
the hook-tendril then is, and were any marked difference 
present, on the removal of turgidity, we should expect to find 
the curvature straighten a little, however slight the straight- 
ening might be. It may safely be assumed, that the curvature 
is due to a difference in the activity of the cambium of the 
two sides, with which a difference of turgidity may, or may 
not, be associated, and to the wood fibres on the convex sur- 
face growing slightly more in length, than do those of the 
concave surface, in support of which conclusion, miscroscopical 
measurements afford distinct corroboratory evidence. 
An interesting point, which at once arises, is, what are the 
actual increases in length, if any, of the two surfaces, concave, 
and convex. In the following experiments, the tendrils were first 
measured, in order to ayoid manipulation as far as possible, 
by taking the exact outline on a piece of paper and measuring 
in millimetres the length of the concave and convex surfaces 
of the outline thus obtained, the final measurements, after 
contact, being taken either in the same way or directly. A 
mark was placed on the hook-tendril, when the first measure- 
ments were taken, to denote the imaginary line of demarcation 
between the apical and basal portions. 
