478 



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



made by the Scientific Instrument Co. In the experiments on 

 curvature the seedlings were cut and fixed by melted cocoa-butter to 

 cork supports in small metal boxes, in which the air was kept damp. 

 They were either placed tangentially at right angles to the axis of 

 rotation, or else parallel to the axis. In the experiments on the 

 distribution of the starch the seedlings were cut and placed in grooves 

 in a sheet of cork, being kept in place by damp filter-paper and a 

 second sheet of cork firmly fixed. In the majority of experiments the 

 tip of the seedling was also fixed to a little bar of wax. The seedlings 

 were fixed radially, the apices of some being inward and of others- 

 outward. This arrangement gives a striking result in successful 

 experiments, for the starch travels to the apical end of the cells in the 

 specimens whose apices point outwards, while it remains basal in the 

 others. 



(a) Experiments on Curvature. 



We give our results in the form of a summary instead of publishing 

 the details of each experiment. It will be seen that there was a good 

 deal of irregular nutation ; this is a drawback to the use of Sorghum 

 and Setaria, but these plants being otherwise convenient we continued 

 to employ them. 



Adding together the results obtained with centrifugal forces of 

 0*02 g., 0-03 g. and 0"04 g. we find that 



85 seedlings (68 per cent.) curved to the centre (apogeotropically). 

 18 „ (14*4 per cent.) did not curve at all. 

 22 „ (17*6 per cent.) curved away from the centre (pros- 

 geotropically). 



We conclude from these results that seedlings of Soi-ghum and 

 Setaria are to some extent stimulated geotropically by a centrifugal 

 force of from 0*02 — 0*04 g. The average amount of apogeotropic 

 curvature to the centre is only 20°, and as this is the result of about 

 22 hours stimulation, we are justified in believing that under our 

 conditions a definite geotropic curvature cannot with any certainty be 

 produced with centrifugal forces of much less value than 0*02 g. 

 The fact that observers working with different plants and by other 

 methods have found curvature with considerably weaker centrifugal 

 force, does not concern us, since our investigation is a comparative one. 



(b) The Behaviour of the Statoliths to Centrifugal Force. Horizontal Axis. 



In the first series the seedlings were all placed radially with the 

 apex outwards for 22 — 24 hours. The behaviour of the starch is not 

 uniform in the cells of the cotyledons, so that it is only possible to 

 give a general impression of the results. 



