1912] BRUSH—MECHANICAL TISSUE 471 
and compared, each being labeled so that it could not be told 
during the examination which was from a tension and which from 
a tension-free tendril. In every case it was possible to decide 
with certainty which one had been under tension from the appear- 
ance of the pith, and each decision was later verified by referring 
to the record. The walls of the pith were in most cases thickened 
in a marked manner to the very center. Measurements with a 
planimeter show the tension-free tendril to have the greater area 
of xylem, while the tension-tendril has the greater amount of 
mechanical tissue when thick-walled pith is included. Com- 
parative areas were found to be as follows: 
| Xylem | Pith (thick-walled) | Total 
Under tension (23) 5 2.61 2.95 5.30 
‘Pension-free ss ao ee ee 4.51 ae 4-51 
In these experiments, as in the others where tension was used, 
a marked characteristic of the sections of tension-free tendrils 
was that the pith was found more or less displaced by the process 
of sectioning, while in those from tension-tendrils the pith held 
its shape as if firm. 
In all these tendrils it was noted that tendrils which had been 
under tension were more rigid and much harder to cut through 
than those free of tension, as noted in the preceding experiments. 
Sections were taken also through the basal third of these same 
tendrils. A close resemblance was found between sections in 
these two regions (middle and base) in the same tendril. In the 
basal part of the tendril in which the middle third had been under 
tension, the diameter of the mechanical tissue is smaller and the 
pith thick-walled throughout, while in the tendril tension-free the 
pith is very thin-walled in the corresponding region. This shows 
remarkably how the stimulus for growth may be transferred through 
the tissues to a part which has not received the stimulus directly, 
since the basal part in neither case in these experiments was under 
tension. 
4. Study of sections; experiments on basal third.—Sections of 
tendrils in which the basal third was tested were studied with the 
