EFFECTS OF GRAVITY, ELECTRICITY, ETC. 201 



the centre of gravity of the earth. The terminal biul of such a stem grows away 

 from the centre of the earth liere just as it does at our antipodes, while the apex of 

 the primary root tends towards it ; and no other force than the gravitation of the 

 earth is conceival)le wliich could bring about this behaviour of the growing parts of 

 plants. Further consideration also shows that this is true for all parts of the plant, 

 no matter under what angle they grow with respect to the horizon or the radius of 

 the earth. Each organ of a plant has its specific irritability as to the direction in 

 ■which it is met by gravity ; and this in such a manner that it only obtains a definite 

 position of equilibrium or rest when it is intersected by the vertical at a certain de- 

 finite angle. It would be simply impossible for any one acquainted with this fact to 

 imagine how the vegetable world could be formed, or exist in general without this 

 effect of gravitation on the processes of growth, if we were not in a position entirely 

 to neutralise the effect of gravitation on a living plant, by means of a simple 

 instrument — the Klinostat. It suffices to fasten the plant in any position whatever on 

 an exactly horizontal axis, and to keep it slowly rotating, so that the growing 

 organs continually change their direction with respect to the horizon, and come into 

 reversed positions during equal periods. In this case the stimuli act in opposite 

 directions on the same organ, and the angles under which the various organs grow 

 forth from their mother-organs are only determined by internal forces. In a similar 

 manner, moreover, the so-called heliotropic curvatures effected by light can also be 

 set aside by continual rotation opposite the source of light. 



Relatively little is as yet known concerning the influence of Electricity on the 

 fife of the plant ^ Experiments have been made chiefly on the action of induction 

 shocks on protoplasm, and on the irritable and motile foliar structures of many plants ; 

 but the results obtained have not afforded a deeper insight into the nature of plants. 

 In general, all that can be said is that very feeble constant currents or induction 

 shocks during short periods produce no visible effects on protoplasm, but that, on the 

 other hand, with a certain strength of the currents, disturbances appear in the 

 protoplasm which resemble those brought about by a high temperature, and that 

 with still further increase of strength of the current the protoplasm is killed. Feebler 

 induction shocks act on the irritable organs of the leaves of Mimosa, the stamens of 

 Berberis, Centaiirea, etc., like shaking or contact — i. e. the organs perform the 

 corresponding movements. I found that constant currents proceeding outwards 

 from the pistil in the flowers of Berberis stimulate the anthers to irritable mo\ements, 

 whereas similar currents in the opposite direcdon are without effect. 



That electro-motive mechanisms are present also in the normal life of the plant 

 itself may be in part directly demonstrated, in part presumed on general grounds. It 

 has been established, for instance, that every movement of water in a tissue, even in 

 the woody mass, is connected with slight electric disturbances; and that these even 

 appear when displacements of water are caused by the mere passive bending of a por- 

 tion of a plant, or by movements of irritability on its part — processes of which we shall 

 treat still more in detail in the proper place. In addition, however, we may assume 



' I collected what was known up to the year 1S65 on electrical mechanisms and efTects in 

 plants in the ' Experimcntal-physiologie' (1S65), p. 74. Kunkel made more recent reseai-ches in my 

 laboratory, and at my suggestion, on the electrical action and conductivity of the living parts of 

 plants — 'Arbeiten des bot. Inst, in Wzbg.,' B. II, p. i and p. 333. 



