HooKER: MOVEMENT IN DROSERA ROTUNDIFOLIA 401 
ditions, of pressure-distribution, tissue-tension, etc., which are 
established in the cells on opposite sides of the originally straight 
organ as a result of an attempted or executed reaction.” 
The inequality of conditions that should constitute tlie auto- 
tropic stimulus may be found in the changes produced:by the dif- 
ference of osmotic concentration observed in bending roots and 
tentacles, since just such a difference induces an analogous reaction 
in hydrotropically stimulated roots. It has been emphasized 
elsewhere (Hooker, 16, p. 21) that the increase in the rate of 
growth which produces the unbending of Drosera tentacles pro- 
ceeds in the same manner as that which causes bending, in both 
cases commencing near the base and extending apically. More- 
over, the amount of growth that occurs during unbending is nearly 
the same in amount and is distributed in much the same manner 
as during bending, so that the unbent tentacle is straight and 
reaches approximately the same position it held before the re- 
action. This nice regulation is intelligible when we consider that 
the changes resulting from the decrease in osmotic concentration 
during bending are directly proportional to the increase in volume 
of the growing cells. It is not to be denied that other factors may 
coéperate in producing the autotropic reaction, but the striking 
similarity with hydrotropic reactions indicates that the effects of 
the difference in osmotic concentration during bending are most 
significant. 
When an insect is caught and digested, the unbending of the 
tentacle is postponed a considerable time, occasionally several 
days. It would appear that the absorption of food material 
through the gland inhibits the reaction to the inequality of con- 
ditions produced by the bending. All the cells of the tentacle 
from base to apex are generally aggregated while food is being 
absorbed. According to Gardiner (’85) the state of aggregation 
is accompanied by a loss of water and he found that the injection 
of water into the tissue stopped aggregation at once and restored 
the cells to their normal condition. This probably accounts for 
the fact that the osmotic concentration in the cells of bent tentacles 
is higher than under any other circumstances. When absorption 
ceases, aggregation stops and the tentacles unbend in the normal 
manner. This is brought about by increased turgidity of the cells 
