480 



Mr. F. Darwin and Miss D. F. M. Pertz. [May 30, 



wards. In one (0*05 g.) the difference was not distinct, while in the other 

 four experiments the difference was distinct. This proves that the starch 

 moves under the influence of a centrifugal force of from 0*03 — 0'04 g. 

 From the prevalence in our notes of such phrases as " scattered and 

 apical," " scattered and basal," it is evident that with 0'03 and 0'04 g. 

 the starch does not move easily, and this is precisely what we should 

 have expected from the small amount of curvature produced with 

 centrifugal forces of about this magnitude. 



Centrifugal Machine with Vertical Axis. — We made some use of a 

 centrifugal apparatus with a vertical axis, in the belief that the 

 results would be more easily observed than in the case of a hori- 

 zontal axis. Supposing that the seedlings are fixed radially on the 

 horizontal disc of the machine, the starch grains will, if the wheel 

 is at rest, be "lateral," i.e., will lie on the longitudinal cell walls which 

 are now horizontal. When the wheel is set in motion there will 

 be no tendency to general diffusion of the statoliths, which will 

 remain " lateral " but will tend to accumulate at the outward extremi- 

 ties of the cells ; the starch will be what we call " apically cornered " 

 or " basally cornered," according as the apices or bases of the seedlings 

 are outwards. 



With regard to curvature, if the seedlings are placed horizontally 

 and tangentially, they will of course curve upwards in response to the 

 force of gravity, and at the same time inwards in response to centri- 

 fugal force. In a similar way, if the seedlings are placed vertically 

 they will not grow straight upwards as they would if gravity alone was 

 in question, but again slightly towards the centre. In those experi- 

 ments in which the centrifugal force varied between 0*02 and 0*04 g., 

 only 48 per cent, of the seedlings curved to the centre, and the average 

 curvature was only 10°. This, perhaps, was to be expected when the 

 centrifugal force was no more than from 2 — 4 per cent, of gravity. 



The effect on the starch grains is shown in Table III. 



Table III. 



Plant. 



Centrifugal 

 force. 



Temp. 



Apex of 

 seedling. 



Position of starch. 





g- 

 0-02 



0-02 



0-03 



°C. 

 18 



19 



16—18 



Out 

 >> 



>3 



Scattered, apical - cornered, 

 and some basal-cornered. 



Lateral and apical -cornered; 

 some basal -cornered. 



Lateral ; some basal and 

 apical-cornered. 







On the whole, with 0*02 and 0'03 g. the movement is irregular and 



