MICHIGAN ACADEMY OF SCIENCE. 
43 
THE INFLUENCE OF TENSION BY PULL ON THE FORMATION 
OF MECHANICAL TISSUE IN THE STEMS OF PLANTS. 
John S. Bohdner. 
In as much as this paper will appear in full elsewhere, it will be sufficient 
to give here an abstract only. 
Purpose: It was my purpose to add further and more conclusive ex- 
perimental evidence to the knowledge of the reaction of actively growing 
stems to tension by pull along their longitudinal axis. To this end, 135 
stems subjected to tension and as many controls, were tested at the end of 
experimental periods, for their breaking strength. An anatomical study 
of the most of these stems was also made. 
Methods: Tension was applied to the experimental stems by means of 
a fastening on the stem, from which strong cords were run over a light run- 
ning pulley, suspended directly over the plant. Weights were then attached 
to the free ends of the cord. The stems were broken at the end of the ex- 
perimental period by pull along their longitudinal axes. This was accom- 
plished by means of an apparatus constructed for this purpose. The amount 
of xylem, and of hard bast was measured by means of a projection apparatus 
and a polar planimeter; also by means of an ocular micrometer, and by 
camera lucida drawings, which were made on standardized bristol board. 
These drawings were then carefully cut out and weighed on a chemical 
balance. 
Results: Stems of Helianthus annuus, Sinapsis alba, Phaseolus vul- 
garis, Ricinus communis, Vicia faba and Vinca major subjected to tension 
showed a higher breaking strength than did like stems used as controls. 
This increase over the breaking strength of the control varied from 5 to 55 
per cent for different experiments. In every case, there was also an in- 
crease of xylem or of hard bast and in most species of both. 
Rubus occidentalis and Lupinus albus stems were also experimented 
upon. The former showed an increase of hard bast but a decrease of xylem 
in the experimental stems as compared with the controls, and the latter, 
an increase of both these mechanical tissues. The breaking strength of 
these stems was not determined. 
Botanical Laboratory of the University of Michigan. 
