1904] 



Notes on the Statolith Theory of Geotropism. 



477 



" Notes on the Statolith Theory of Geotropism. I. Experiments 

 on the Effects of Centrifugal Force. II. The Behaviour of 

 Tertiary Boots." By Erancis Darwin, E.B.S., and D. F. M. 

 Pertz. Eeceived May 30 —Bead June 9, 1904. 



I. 



According to the statolith theory,* there are in plants certain cells 

 specialised to act as organs of orientation in space ; organs, in fact, 

 functioning like the otocysts of certain animals. In both cases the 

 sense of verticality is believed to be the result of the pressure of 

 certain heavy bodies (usually starch grains in the case of plants), on a 

 sensitive surface, namely, the lining membrane of the otocyst in the 

 case of animals, or in the case of plants the protoplasm lining the 

 statolith-containing cells (statocytes). 



In a paperf dealing with the arguments for and against the theory, 

 Jost brings forward as the most serious objection the behaviour of 

 plants to centrifugal force. He found that plants, subjected to 

 centrifugal force equal to from 0*02 — 0'05 g.,} exhibited curvature, but 

 that the starch-grains were uniformly distributed throughout the 

 statocytes, not, as should be the case according to our theory, resting 

 on the cell walls furthest removed from the axis of rotation. Jost 

 sees in these results an absolute proof that, in the cases investigated 

 by him, the starch grains do not function as statoliths. 



It seemed to us that this conclusion was a somewhat hasty one and 

 we determined no longer to delay the investigation of Knight's 

 experiment in relation to starch grains, which we had previously 

 recognised as a necessary part of the statolith question. Our experi- 

 ments were carried out on seedlings of Setaria and Sorghum, in which 

 the statoliths are in the cells of the cotyledon (coleoptile), and in 

 which the position of the movable starch can easily and rapidly be 

 determined by splitting the cotyledon longitudinally and examining 

 the two halves mounted in iodine solution. The experiments were 

 directed to two points, viz., the centrifugal force needed to produce 

 (a) geotropic curvature, (b) movement of starch-grains. It will be 

 seen that our results are directly opposed to those of Jost, inasmuch 

 as, according to us, the lowest effective centrifugal force is about the 

 same in the two sets of experiments. The centrifugal apparatus was 

 driven by a hot-air engine regulated by one of Griffiths's gas-regulators 



* Noll, ' Heterogene Induction,' Leipzig, 1892 ; Haberlandt and NSmec, ' Ber. 

 Deutschen Bot. Gesellsch.,' 1900. 



f "Die Perception des Sclrwerereizes in der Pnanze, : ' 1 Biolog. Centralblatt,' 

 toI. 22, March 1902, p. 161. 



X g. being the acceleration of gravity. 



VOL. LXXIII. 2 L 



