398 HooKER: MOVEMENT IN DROSERA ROTUNDIFOLIA 
cell-walls do not always return to their original condition, but are 
frequently crumpled or wrinkled. The rate of change in the cell- 
wall properties undoubtedly increases during the inflexion. In 
the same way the decrease in osmotic concentration which results 
from the increase in volume of the elongating cells is soon compen- 
sated for by the formation of new osmotically active material, as 
is shown by the equality of osmotic concentration on opposite 
sides of the tentacle a short time after it has become fully bent. 
This process too is probably initiated soon after inflexion begins, 
with the result that no marked difference in osmotic concentration 
is noticeable on opposite sides of tentacles which bend slowly. In 
the last analysis, therefore, the growth which causes the inflexion 
of Drosera tentacles is the activity of the protoplasm in manu- 
facturing cell-wall substance and osmotically active material. 
2. COMPARISON WITH GEOTROPIC MOVEMENTS 
The movement of Drosera tentacles is seen to be brought about 
by the same mechanism found in geotropically reacting organs, 
where Kraus (’82, p. 87) and Noll (’88, p. 511) observed a decrease 
in the osmotic concentration of the cells on the convex side of 
roots and stems, which was particularly evident in case of rapid 
bending. The subject is well summed up by Jost (’13, p. 580) in 
the following paragraph, and his remarks apply to the bending of 
Drosera tentacles with equal felicity: 
In all cases that have been more carefully studied, the immediate cause of the 
bending is a difference of growth in length on opposite sides. The surface growth of 
the membranes here as elsewhere is preceded by stretching aa to santas: and this 
is gradually made permanent by growth. If an organ be plasmolyzed at the be- 
ginning of the geotropic bending it Snsgred — ie ee but repeal? ate ae 
is permanent. The stretching is This 
difference might consist in an ined: osmotic pressure on ise convex side and 
the convex _. peers — ein ued =_— is rise so sorgeccumte, Bok are 
we consider 
pressure, but that this latter frequently depends on the increase in cell-volume. 
The unequal stretching of the opposite sides due to turgidity must therefore be 
connected with an alteration in the elasticity of the ee p the convex side be- 
ming more extensible. Of course in unicellular ns (in sporangiophores of the 
Poser tae for example), the bending must pasliast ewig on a change in the elas- 
ticity of the cell-wall. 
