396 HooKER: MOVEMENT IN DROSERA ROTUNDIFOLIA 
during bending is given in a previous paper (Hooker, ’16). 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 (zbid. Table III, 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. 
