1903.] 



The Statolith-tkeory of Geotropism. 



365 



the tip containing the statocytes have been removed, the capacity for 

 geotropism returns with the regeneration of the statoliths. Even 

 here — though the fact is a striking one — the argument seems to require 

 the heliotropic test. For obviously the regeneration of the tip may 

 mark the recovery of a generalised sensibility, and not merely the 

 rehabilitation of the special gravitational mechanism. The same 

 objection holds to some extent with regard to Haberlandt's* experi- 

 ments on plants found to be starchless in winter. It should have been 

 more definitely shown that they are heliotropically active though 

 incapable of gravitational reaction. 



The Tuning-fork Method. 



In the autumn of 1901, I began a series of experiments by a method 

 which was at the time a new one, but has been in the meanwhile 

 published by Haberlandt.j It seems to me that Haberlandt's argu- 

 ment is open to the objection above set forth, and as it is an objec- 

 tion I have tried to meet, my results seem to be worth giving. 



My point of view was that if gravitational sensitiveness is a form 

 of contact-irritability (which must be the case if the pressure of the 

 statoliths on the plasmic membrane is the critical event), then it might 

 be possible to intensify the stimulus by vibration. I hoped, by 

 applying vibration in a vertical plane to a horizontal seedling, to 

 make the starch grains dance on the lateral walls, and by such 

 repeated blows on the protoplasm to produce more active geotropic 

 response. 



The experiments were made with seedlings of Sorghum, Setaria, and 

 Panicum. In the earlier trials entire seedlings were used, but they were 

 found difficult to fix horizontally with sufficient accuracy, and I 

 consequently employed cut hypocotyls cemented by means of melted 

 cocoa-fat on cork supports, and kept damp in small metal boxes, each 

 containing a strip of wet filter-paper. 



The vibration was supplied by means of a tuning fork driven by an 

 electric escapement. The fork was fixed in a horizontal plane so that 

 the vibration was vertical. The amplitude of the vibration varied in 

 different parts of the fork from 4 mm. to less than a millimetre. The 

 rate was about 47 vibrations per second. 



The general plan of the experiments was to attach a pair of metal 

 boxes, one to each limb of the fork, each box containing four to six 

 seedlings fixed approximately horizontal. Control boxes were placed 

 on a support a few centimetres from the fork. It was found essential 

 to insure an identical temperature for the experimental and control 

 plants. The fork is set in motion and the experimental plants sub- 



* Haberlandf", ' Pringsheim's Jahrbuclier,' 1903, p. 472. 

 f Loc. ext. (1903), p. 489. 



2 D 2 



