ie 
‘ 
| 
: 
1907] HIBBARD—FORMATION OF MECHANICAL TISSUE 363 
Woreirzky (’87), in his “ Vergleichende Anatomie der Ranken,” 
gives the results of weighting experiments, and comes to the same 
conclusions as voN DerscHau. He found, by comparing weighted 
tendrils of Passiflora quadrangularis which had secured attachment 
with weighted tendrils which had not, that the tensile strength of the 
former had increased about twice as much. With tendrils-of Cur- 
curbita Pepo the resistance to strain was increased thirteen fold. 
This he believed was not the result of pull alone, but one of pull and 
contact combined. 
NEWCOMBE (’95, p. 446), speaking of the reaction of tendrils to 
contact, states “that the first strengthening tissue is here laid down 
as a response to contact; its increase is the regulatory response of the 
plant to the strain that it feels.” 
MacDoveat (’96, pp. 377, 378) believes that contact stimuli are 
not transmitted beyond 2 or 3™™ and, as the thickening of the tendril 
always takes place after contact, we are left to conclude that it is due 
to the pull or traction exerted by the weight of the stem supported by 
the tendril. 
PEIRCE (:04, p. 241) believes also that the strengthening of the 
free basal portion is not due to contact, but to the pull exerted in 
bringing the stem nearer the support. 
Firtinc (:03, p. 476) has lately shown that contact stimuli are 
transmitted for some distance, and for that and other reasons their 
effect on the basal portion of the tendrils cannot be excluded. It 
thus becomes a question how much of the increase of strength is due 
to pull and how much to contact. 
Vécutinc (:02) investigated the influence of pull on sunflowers 
and cabbages that had been prevented from flowering by means of 
decapitation, and found that no new tissue had been formed and that 
No increase of mechanical tissue had occurred as a result of the pull. 
WIEDERSHEIM (:03) finds that the expected development of new 
tissue and the thickening of the wood and bast fibers in weighted 
pendent branches of F raxinus, Fagus, Sorbus, and Ulmus does not 
occur. On: the other hand, in Corylus he observed an increase in 
the number of bast fibers. This he attributes to a self-regulatory 
development. 
BALL (:04) repeated the work of HEGLER. Asa result of numerous 
