A laboratory course in plant physiology, especially as a basis for ecology; . vements connectedwith the process of Growth itself and independent of externalstimuli. One way to test this is by determining whether, inelongating structures, when the one-sided influence of light,gravitation, etc., is shut out, the growth is in straight lines. MOVEMENTS. 113 73. Is the growth of elongating structures, apart from re-sponses to lateral external stimuli, exactly in the line of their axes,or does it show lateral movements? Answer by Experiment 42. EXPERIMENT 42. This may be determined by placing a plan
A laboratory course in plant physiology, especially as a basis for ecology; . vements connectedwith the process of Growth itself and independent of externalstimuli. One way to test this is by determining whether, inelongating structures, when the one-sided influence of light,gravitation, etc., is shut out, the growth is in straight lines. MOVEMENTS. 113 73. Is the growth of elongating structures, apart from re-sponses to lateral external stimuli, exactly in the line of their axes,or does it show lateral movements? Answer by Experiment 42. EXPERIMENT 42. This may be determined by placing a plant insuch a position that the chief external stimuli, light, gravitation,heat, and moisture, cannot exert a lateral stimulus upon its elongatingstem, and by arranging a system of sighting along the axis of thestem so that the smallest deviation from a straight line will be madevisible. The former maybe accomplished well enough for all prac-tical purposes by placing the plant (one growing rapidly with a ver-tical stem) on the table of a well-lighted greenhouse, and surround-. FIG. 29.—SIMPLE ARRANGEMENT FOR THE STUDY OF CTRCUMNUTATION. One-fourth the true size. ing it by a black-paper cylinder which rises three or four inches aboveits top. To accomplish the latter, some method must be employedwhich will both allow the exact direction of the axis to be sighted,and also will magnify the slightest lateral movement, and permit it H4 PLANT PHYSIOLOGY. to be recorded. Prepare a recording glass supported by a tripod asshown in Fig. 29, the glass being some ten inches above the the slenderest glass filament (see page 39) you can, 2 ; place a tiny bead of black wax on one end, and slip about ahalf cm. up the other a tiny circle of white paper with a tiny blackspot in the middle through the center of which passes the this filament vertically to the side of the top of the stemwith shellac, bead upward. Sight through the glass plate, bringingthe bead an
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