Effect of Tension on Plants. 
97 
We have thus to deal with two different stimuli, which produce analo- 
gous results, and which may combine in their actions. 
In this manner are the results to be explained which appear when 
a forcibly bent stem is so placed that the plane of the curve is horizon- 
tal. Under these conditions it appears that the action of gravitation 
predominates, since only the zenithward side underwent thickening of 
the cell walls. Such a result is very well possible, since in physiological 
processes, the resultants do hot correspond to a simple summation of 
the isolated individual factors, but rather, as experience shows, the 
different factors, working among themselves, may influence and modify 
each other. Dislocations and modifications appeared in the rythmical 
bending of stems in two directions, in so far as the thickening of cell 
walls was not confined to the two flanks but extended to the sides so that 
a continuous cell wall thickening appeared. Whether the tensile strength 
was also increased in this case was not investigated. 
EXPLANATION OF FIGURES. 
All figures were drawn with the Abbe camera and reduced to four- 
fifths by the engraver. Mag. 150. 
Fig. 1. Upper side of a section through a stem of Ricinus com. 28 
days old and 21 days horizontal and stretched. 5 cm. from ground. 
Fig. 2. Under side of the same section. 
Fig. 3. Section/ of a normal Ricinus of the same age and at the 
same distance. 
Fig. 4. Upper side of a cross section of a stem of Ricinus of the same 
age which was horizontal and forcibly bent over a glass rod for 21 days. 
About 5 cm. from ground and 2 cm. from the point of contact with the 
rod, toward the root. 
Fig. 5. Lower side of the same section. 
Fig. 6. Bast, collenchyma and bark from the upper side of a 15-day 
old epicotly of Phasaeolus multiflorus which was enclosed in a plaster 
of Paris cast and laid horizontal for 7 days. 
Fig: 7. The same tissues from the under side of the same section. 
Fig. 8. Cross section through a 21-day old stem of Phaseolus mult, 
which was bent in two directions for 7 days on the “rocking machine.” 
Taken from the point of strongest bending. P — cambium-like cell pro- 
liferation in the parenchyma. 
Fig. 9. Section from a normal Phaseolus of same age as the preceding 
and taken at the same height. 
