CENTRIFUGAL FORCE. THE KLINOSTAT. 683 



necessitates much more complicated intellectual exercise than the reflections given 

 above, which lead to the same conclusions much more simply. 



It will probably be not undesirable for the reader to learn, at least as an 

 example, how the action of centrifugal force on the direction of growth of the 

 organs of plants can be demonstrated, and this more conveniently than Knight 

 did it. I refer therefore to Fig. 384 and its explanation. 



If, then, it is gravitation, which we suppose to be situated in the centre of 

 gravity of the earth, so to speak, and the action of which takes place in the direction 

 of the earth's radius, or, what is the same thing, in the vertical line, it must be 

 possible to nullify this action by compelling growing plants to continually alter their 

 direction with respect to the vertical, in such a manner that the gravitation acts 

 on the symmetrically opposite sides of a growing part of a plant for equal periods 

 in opposite directions. Starting from this reflection I constructed an apparatus 

 which I called the Klinostat. This apparatus, which may be constructed in very 

 different ways, has essentially the one object of slowly rotating, by means of clock- 

 work or other motive power, a solid rod of wood or metal which must be exactly 

 horizontal, and this so that a rotation is completed in 15-20 minutes. On this rod 

 (i in Fig. 385) growing plants, e. g. seedhngs, may be so fixed that they participate 

 in the rotation of the rod without hindrance to their further growth. It matters not 

 in what direction the growing organs are fastened on the rotating axis as long as the 

 rotation is equable, so that every growing part of the plant turns the same side up- 

 wards as well as downwards during equal periods of time, so that the influence pro- 

 ceeding from the centre of gravity of the earth must act on the growing portions of 

 the plant during equal periods in exactly contrary directions. If this occurs, no action 

 of gravitation whatever can make itself effective on the direction of growth, since a 

 longer or shorter time is necessary for this, and before the part of the plant has had 

 time to make a curvature downwards or upwards, it finds itself already, in conse- 

 quence of the rotation, again in a position which would necessitate its making the 

 exactly contrary curvature, and thus no curvature at all is accomplished : it goes 

 on growing in exactly the direction arbitrarily given to it when it was fastened to 

 the axis. 



After these preliminary remarks, I may now attempt to describe more exactly 

 the processes which take place during the geotropic curvatures upwards or down- 

 wards. Here I find myself in the agreeable position of being able to depend, step 

 by step, on my own very detailed investigations. 



We may first consider the upward curvature of shoot-axes which normally grow 

 erect. 



My observations have been made chiefly with the thick, rigid, long internodes of 

 such flower-stalks as attain considerable heights in short periods, and the smooth 

 surfaces of which admit of being marked with Indian ink, and of exact measurement 

 of the marked portions. The measurements on the straight shoots, as well as on the 

 concave and convex sides of curved ones, were accomplished by means of* flexible 

 rules stamped on stiff paper. 



In order to be able to criticise the processes during the up-curving of shoot-axes 

 it is necessary to be previously acquainted with the distribution of growth in them : 

 this has already been described in Lecture XXXII. At first the whole internode, as 



