— 136 — 



Before giving the results, a few details may be noted. In the 

 figure it will be seen that the seediing is oblique to the axis ; this 

 arrangement, in which we follow Piccard, is obviously necessary, 

 since if the seediing were at right angles to the axis the geo- 

 stimulus would be theoretically nil, and practically would be very 

 small. I aimed at fixing the plant at 45" to the axis but in practice 

 the angle varied. In Piccard's experiments, which were made on 

 roots, the seed was fixed and the tip of the radicle projected 

 beyond the axis. He was only able to keep the plants in rotation 

 for one hour, becaiise owing to the growth of the nadicle the 

 relative positions of the tip and growing region changed. But in 

 my experiments i could continue the experiment for many hours 

 because if, by its growth, the cotyledon comes to project slightly 

 beyond the axis as shown in the figure, the result is a favouring 

 of the hypocotyl, since its growing region is thus carried further 

 from the axis and in this way subjected to increased centrifugal 

 force. The seedlings were kept moist by a small well-fitting bell 

 jar containing a small quantity of water, and screwed firmly to the 

 diso D. They were subjected to a temperature of 25 — 30^ C. It was 

 not thought necessary to place the apparatus in the dark as the 

 axis of rotation was parallel to the Windows and moreover the 

 cotyledons were darkened by the thick layer of gypsum by which 

 they were attached to the plate. In all but the first three experiments ^) 

 the axis of rotation was strictly horizontal, and even had not this 

 been the case it is hard to believe that plants rotating nine or ten 

 times a second could be affected as though they were on Fitting's 

 oblique klinostat. 



There is a small difficulty in expressing the centrifugal 

 force to which the cotyledon is exposed since it increases from zero 

 at the base to a value at the apex depending on the length of the 

 cotyledon and its angle with the axis. If the cotyledon is 10 nmi 

 in length and makes an angle of 45^ with the axis, the distance 

 of the apex from the axis = 10X0707 = 7*1 mm. With a rotation 

 of ten times a second, this will give a centrifugal force equal to 

 2*8 (j at the apex of the cotyledon. It must be remembered that the 

 efficient component of the centrifugal force will be less than this 

 because of the obliquity of the plant. In this case the component 



•) In these the cotyledons were fixed in glass tubes and not therefore 

 darkened. 



