Septembeb 16, 1904.] 



SCIENCE. 



377 



their behavior toward gravitation. The revo- 

 lution must be so slovp therefore as not to bring 

 in the centrifugal eiiect. Czapek* has meas- 

 ured the sensitiveness of plants to centrifugal 

 force when gravitation is neutralized, finding 

 that by sufficiently long continuance of the 

 experiment, curves will come when the rate 

 of revolution gives an acceleration exceeding 

 one thousandth part of the acceleration of 

 gravitation (.001 g.), but do not appear, at 

 least for many hours, at a lower rate of speed. 

 The relation of the acceleration due to rota- 

 tion to the acceleration of gravitation is 

 found by the formula F = 4.024 r/f, in which 

 r is the distance from the center of rotation 

 in meters, t is the time of one revolution in 

 seconds, and F is the ratio of the acceleration 

 of rotation to the acceleration of gravitation. 

 By applying the formula it will be found 

 that an object rotating once in twenty seconds, 

 at a distance of 10 cm. from the center will 

 have an acceleration approximately equal to 

 .001 g. Such a rate of revolution would, 

 therefore, be within the limit of safety for 

 objects less than 10 cm. from the center of 

 rotation. To make the results doubly sure, 

 one could keep a speed not to exceed one 

 revolution per minute. 



Avoidance of too Slow Revolution. — Not 

 only is there an upper limit of speed, but a 

 lower limit also when one wishes to neutralize 

 the tropic effect of light or gravitation. A 

 revolution that is so slow as to allow a plant 

 to remain in one quadrant of its path, or, in 

 certain cases, in one semicircle, for a period 

 equal to the period required to produce a 

 curvature when the plant is at rest, will pro- 

 duce a curvature of the plant on the klinostat, 

 in which the apex of the plant member will, 

 by combining its curves during a complete 

 revolution of the klinostat, describe a line, 

 as it moves back and forth, or a circle as it 

 circumnutates, the one or the other accord- 

 ing to the position of the plant with reference 

 to the axis of revolution of the klinostat. In- 

 deed, the recent work of F. Darwin and Pertzf 

 may be taken to indicate that a plant on the 

 horizontal klinostat, remaining in a quadrant 



* Jahrl. iciss. Bot., XXVII., 1895, 243. 

 f Annals of Boiany, XVIL, 1903, 93. 



for a period even less than the latent period 

 of curvature may keep up a rhythmic oscilla- 

 tion as it revolves. Since at a temperature of 

 20° C. the latent period for curvature of some 

 roots and stems is not over twenty minutes, 

 and the perception period of some plants for 

 gravitation at 20° C. is less than fifteen 

 minutes, safety would advise that thirty 

 minutes should be the limit for slow revolu- 

 tion, the plant then being in each quadrant 

 but seven and one half minutes. 



Not All Tropic Influences can he Neutral- 

 ized hy the Klinostat. — It is often desirable 

 to revolve a plant on the klinostat, thereby 

 freeing it from the tropic effect of gravitation 

 in order that some property of the plant, 

 ordinarily veiled by the control of gravitation, 

 may be brought to expression. Thus the bend- 

 ing of several roots from light has been dis- 

 covered by the use of the klinostat, the same 

 roots showing no response to light as long as 

 the stronger influence of gravitation was oper- 

 ative. It is well to know, however, that the so- 

 called autotropism of plants is uninfluenced 

 by the klinostat, and that this tendency of 

 plants to grow straight must always operate 

 against the formation of curves in plants that 

 might otherwise show responses. This auto- 

 tropism of roots and stems is of no incon- 

 siderable moment, since curves of several 

 hours' formation are by it completely obliter- 

 ated while the plant is so revolved on the 

 klinostat as to neutralize the tropic effect of 

 gravitation. 



It is of the first importance to know that 

 only those parts of plants which are physiolog- 

 ically radially symmetrical will grow straight 

 while revolving on the klinostat with hori- 

 zontal axis.* A plant may be radially un- 

 symmetrical toward gravitation, in which case, 

 revolution on the klinostat will not release it 

 wholly from the tropic influence of gravita- 

 tion; or it may be radially unsymmetrical 

 physiologically because of unsymmetrical be- 

 havior due to internal stimuli. In the revolu- 

 tion of the latter kind of plant member on the 

 klinostat (many leaves), we may have curves 

 due to unequal growth on the one side or the 



* Noll, Jahrh. imss. Bot., XXXIV., 1900, 459. 



