1912] BRUSH—MECHANICAL TISSUE 457 
while those from different vines have different areas. The relia- 
bility of this method of securing controls is also shown by a com- 
parison of the breaking strength of tendrils from the same and from 
different vines, which shows tendrils on the same vine under the 
. same conditions to correspond quite closely in tensile strength. 
Measurements were also taken to secure proper controls, but 
it was found that healthy tendrils on the same vine varied only 
slightly in rate of growth, and were ready for contact at approxi- 
mately the same age. As the time when the tendril is most suitable 
for contact can be judged within 24 hours, and since the time 
between the maturing of tendrils on successive nodes is quite 
constant, a very uniform method of starting the experiment on 
each tendril was obtained. Moreover, when tension was applied, 
a certain scheme for weighting was used, to secure gradually 
increased tension at the same rate in each case. The experiment 
on each tendril was closed at exactly the same length of time from 
the date when it was begun, and note of weather conditions was 
taken during the time of experiment. 
Tendrils which had been under experiment were compared by 
two methods: (1) by their breaking strength, and (2) by their 
anatomical structure. The breaking strength was obtained by 
wrapping the extremities of the portion to be tested with damp 
cotton dipped in plaster of Paris; each end was then fastened 
between a pair of wooden blocks, made for the purpose, which 
were screwed tightly together; this preparation was then placed 
on a machine for breaking; one of the blocks was connected to a 
rod on which a thumbscrew was turned, to secure gradually increas- 
ing tension; the other block was connected.to a spring balance from 
which was read the degree of tension at which the tendril broke. 
A straight portion of the tendril was always taken for testing. 
When the break occurred at the place of attachment of the tendril, 
the result was thrown out. 
Cross-sections of tendrils were made and microphotographs 
taken at a magnification of too diameters. This shows well the 
form and arrangement of the mechanical tissues. Camera sketches 
of the area of mechanical tissue were also made and compared with 
microphotographs of the same tendrils in the study of the cross- 
