466 BOTANICAL GAZETTE [JUNE 
only about 10 cm. of mercury was necessary to secure the same 
amount of radial pressure that is exerted on the contact portion 
when 20 grams tension is applied to the tendril with the contact 
portion coiled about a support, due allowance being made for the 
pressure taken up by the resistance of the rubber tube. 
Since, however, in spite of the care taken to secure a close 
contact between tendril and tube, the amount of pressure which was 
actually exerted upon the tendril was dependent upon how closely 
the tendril had coiled about the tube, only relatively high pressures 
were used, which were for the purpose of determining the effect 
of pressure alone upon the tendril. A small amount of pressure 
was applied at first and gradually increased. The tensile strength 
of the whole tendril was determined in all experiments on the effect 
of pressure, to see whether an actual increase in the strength of 
the tendril had occurred. The break occurred, with a very few 
exceptions, in the middle third. 
TABLE VI 
PERIOD 28 DAYS 
. INCREASED PRESSURE NorMAL PRESSURE 
Tendril Hg. height Breaking strength Tendril Breaking strength 
Ag . 55 cm. 1085 grams Ay 785 grams 
FE, 975 
E, ee 1775 E, 1025 
iL 22 I1I50 t I Mj 
I; 30 950 ; he 
Lz 20 aks Ly 615 
L, 30 960 L; 625 
M, 45 goo 
M; 30 720 M; 575 
Me 30 1160 
N; 39 O15 
N, 30 850 f Ns 725 
V; 30 700 V, 500 
Averages ferele) 727 
The breaking strengths as shown in table VI show an undoubted 
increase in the strength of tendrils with increased radial pressure. 
That the increase was small in some cases may be due to the failure 
of the tendril to coil about the tubing securely. 
