464 BOTANICAL GAZETTE [JUNE 
ligature in the one under tension; these loops were so arranged 
that they acted against each other (fig. 3), so that when the upper 
one was run over a pulley and a weight attached and a like weight 
hung on the one below, a pressure equal to the 
weight used was exerted radially upon the 
tendril. In order that no injury might be done 
to the tendril, three lengths of soft cotton twine 
were placed lengthwise to the tendril, so that 
they lay between the loops and the tendril; 
this served well to transmit the pressure to the 
surface of the tendril. In only a very few cases 
was the tendril injured by this means. Where 
such injury occurred, the tendril was thrown out of record. In both 
cases attachment was made to the tendril slightly below that in 
the preceding experiment, so that it was just within the proximal 
third of the tendril, to avoid the contact stimulus as much as pos- 
sible, since the sensitiveness of the tendril diminishes rapidly 
toward the base. 
Weights were added as in the preceding’experiment. Breaking 
strengths of these tendrils are given in table V. Four tendrils in 
this series were allowed to grow without any contact whatever, to 
determine the effect of contact-pressure on the basal portion of 
the tendril, and are included in this table; likewise, one tendril 
which had a ligature placed similarly to those in the first two 
columns but without tension or contact-pressure. 
These results are very different from those in the last experi- 
ment, and seem to verify the inferences made as to the real cause of 
the unexpected increase in strengthening tissues in the tension- 
free tendrils in the preceding experiments. That this increase 
did not take place in the ‘‘tension-free”’ tendrils in the experiments 
on the middle third is no doubt due to the fact that the part under 
tension in this case was in the upper or contact portion of the ten- 
dril, which is not so sensitive to the tension stimulus. ‘‘Tension- 
free’ tendrils show an increase in breaking strength over ‘‘free” 
tendrils, while those under tension show a much greater tensile 
strength. This must mean that tension in the lower part of the 
tendrils is effective in giving greater strength to that portion. 
to protect tendril from 
injury. 
