378 MacDongal . — The Mechanism of 
coils in a tendril whose tip is attached to a support often 
begins at a point 25 cm. distant from the point of reception 
of the stimulus at the tip. The attachment of the tip of 
a tendril to a support by curvature exerts no direct influence 
on the free portion of the tendril, except by the traction 
exerted by the weight of the plant-body thrown upon it. The 
formation of the free coils of an attached and of an unattached 
tendril is found to differ only in so far as the effect of this 
mechanical strain is concerned. This is emphasized by 
reference to No. IV of the dynamometric tables, in which 
it is shown that a young tendril continued to elongate after 
its tip had clasped a support, and did not form coils until it 
had attained maturity. It is therefore necessary to exercise 
great care in the delimitation of the processes of curvature by 
which a tendril reacts to stimuli, and the processes of growth 
by which permanent coils are formed, in the analysis of the 
movements of these organs. 
Results Obtained by Various Methods of 
Experimentation. 
In the research directed toward the determination of the 
mechanism of curvature, two methods of experimentation 
have been used in securing the data upon which conclusions 
have been based : — First, estimation of the relative turgidity 
of the tissues of the convex and concave sides by means of 
plasmolysis Secondly, measurement of the distance between 
two points on the convex and on the concave surface of the 
curving organ before and after contraction. In addition to 
a revision of the results obtained by these methods, it is 
proposed to throw additional light on the subject by an 
examination of the structure, form, and arrangement of the 
cells of probable motor zones in the convex and concave sides 
of the tendrils before and after induced curvature. 
Measurement of elongation. Independently of his plasmolytic 
researches, De Vries found by measurements that in encircling 
a support the growth in length of the convex side of a tendril 
