Igo09] BORDN ER—INFLUENCE OF TRACTION ON STEMS 253 
WIDERSHEIM (29) experimented with pendant branches of Fraxi- 
nus, Fagus, Caragana, Sorbus, Ulmus, and Corylus. He fastened 
weights directly to these branches and continued the experiment 
through most of the growing season. Only in the case of Co-ylus 
was there any response; viz., an increase in the number of bast fibers. 
BALL (1) experimented with Helianthus annuus, Phaseolus multi- 
florus, Lupinus albus, Helleborus niger, Ricinus communis, two species 
of Cyperus, and Mirabilis jalapa. His conclusion was that these 
plants do not respond to tension by an increase of their breaking 
strength or by the production of mechanical tissue. 
Hrpparp (12) found an increase of mechanical tissue in the stem 
of Vinca major when the same was subjected to longitudinal pull. 
He failed to find any response in the stems of Helianthus annuus, 
Ricinus communis, Brassica oleracea, and Phaseolus multiflorus. 
Hrsparp did not determine the breaking strength of his stems. 
2. STEMS: THE INFLUENCE OF COMPRESSION; ALSO 
COMPRESSION AND PULL COMBINED 
Knicut (14) tied a young tree in such a manner that it was swayed 
only in the plane of the prevailing wind. After the lapse of one 
growing season, the diameter in this plane was found to be greater 
than the diameter at right angles to the same. 
HIBparp (1 1) found that compression caused a small increase 
of mechanical tissue in the stems of F uchsia, Vinca, and Helianthus, 
while Coleus gave no response. 
3. ROOTS: RESPONSE TO TENSION 
Hipparp (1 I) says: “ Pull in the direction of the longitudinal axis 
of the plant called forth a small increase of mechanical tissue in the 
Main and lateral roots of Helianthus annuus and Ricinus communis.” 
4. TENDRILS AND PETIOLES 
_Darwin (4; Gray 8, p. 176) says that in the grape-vine, 
Virginia creeper, etc., attached tendrils thicken and harden, gaining 
wonderfully in strength and durability, while those which remain 
“nattached soon shrink up or wither and fall off. 
_ Mitier (18) found that contact produced earlier and greater 
lignification of the sclerenchyma, even in the free portion of the ten- 
