. A laboratory course in plant physiology. Plant physiology; Plant ecology. 23° PLANT PHYSIOLOGY The power exerted in geotropic response, together with the very obvious lengthening which accompanies the bending of roots and stems, suggests that the process must be ultimately connected with Growth, and the problem arises: Are ordinary geotropic responses dependent upon growth? This may be determined in either of two ways: first, by arrang- ing all conditions for a geotropic response, but withholding some essen- tial condition of growth (, oxygen, or favorable temperature), and, second, by o
. A laboratory course in plant physiology. Plant physiology; Plant ecology. 23° PLANT PHYSIOLOGY The power exerted in geotropic response, together with the very obvious lengthening which accompanies the bending of roots and stems, suggests that the process must be ultimately connected with Growth, and the problem arises: Are ordinary geotropic responses dependent upon growth? This may be determined in either of two ways: first, by arrang- ing all conditions for a geotropic response, but withholding some essen- tial condition of growth (, oxygen, or favorable temperature), and, second, by observing whether the place of response corresponds with the place where growth is occurring. The first the student may readily plan for himself (with suggestions from Detmer, 448) and the second may be arranged thus: Experiment. Place a strong-growing seed (, Horse Bean) in a wire-and-sphagnum cage and, when the root is 1-2 cm. long,. Fig. 66.—Convenient arrangement for Sachs' geotropic force experi- ment; X h mark it along one side by the roller space-marker (page 197); then place it horizontal, marks upward, in a suitable moist-chamber, and note the relation between the growing and the responding parts. Select a potted plant with slender-growing upright stem, mark it with the roller space-marker, place it with stem horizontal, marks underneath, and note effect of the response upon position of the marks. The localization of response here shown suggests an inquiry as to whether this is confined to growing tips and may not occur elsewhere, a question which can partly be answered thus: Suggested Experiment. Select a growing grass-stem, or the creeping greenhouse Wandering Jew, and cut out a piece some 10 cm. long with a node in its middle. Place the lower end in water, and lay it horizontally, with the node and upper end free, which can be accomplished by thrusting it into a vial filled with wet sphagnum, or else, and better, by the arrange- ment of figure 67, with the pin
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