396 Hooker: Movement in Drosera rotundifolia 



during bending is given in a previous paper (Hooker, 'i6). An 

 average of eleven measurements taken in the region of most active 

 growth shows the increase to be about 27 per cent, of the original 

 length. In one typical example {ibid. f. 6), cells on the abaxial 

 side {ihid. Table HI, segment 5) in the bending region grew from 

 0.45 mm. to 0.57 mm., an increase of 26.6 per cent. Assuming 

 the other dimensions of the cell to remain unaltered, the increase 

 in volume of the cells in this region would be proportional to the 

 increase in length. An increase in volume must be accompanied 

 by a corresponding decrease in osmotic concentration. Thus if 

 the original concentration were eight atmospheres, we should 

 expect as the result of an increase in volume of 26 per cent, an 

 equivalent decrease in osmotic concentration, that is a fall from 

 eight to six atmospheres. When it is considered that the meas- 

 urements of osmotic concentration were taken before bending 

 was completed, and that soon after the tentacle is bent the cells 

 restore their original osmotic concentration, a process that must 

 commence soon after bending begins, we see that the maxi- 

 mum decrease in osmotic concentration observed is amply ac- 

 counted for by the increase in volume of the growing cells. The 

 maximum decrease observed was approximately 25 per cent.; the 

 increase in length averaged 27 per cent.; the correspondence is 

 well within the limits of probable error. The alteration of osmotic 

 concentration is therefore a result of the growth of the cells, and 

 not a determining factor of their elongation. 



No marked change in the osmotic concentration of the cells on 

 the adaxial side of the bending tentacle was observed at any time. 

 The slight elongation or compression which these cells experience 

 during bending is probably insufficient to make a change of osmotic 

 concentration perceptible. The irregularity in the nature of the 

 alterations on the concave side of the tentacle indicates that this 

 side takes no active part in the bending, but is either stretched or 

 compressed according to the mechanical conditions that happen 

 to prevail in the base of the pedicel. Gardiner ('85) states that 

 the cells on the concave side of well-inflected Drosera dichotoma 

 tentacles lose their turgidity at the bending point. No distinct 

 evidence of loss of turgidity by the cells on the concave side -of 

 inflected Drosera rotundifolia tentacles was observed, however. 



