THE NERVOUS MECHANISM OF PLANTS 418 
the regulation of the water supply upon which its con- 
stituent protoplasts are so dependent. 
The immediate result of such an increase of perme- 
ability is that the elastic recoil of the stretched cell 
membranes, which we have seen is a feature of every turgid 
cell, drives some of the water out of the cell, causing the 
latter to shrink. in volume. 
The effects of stimulation may be seen in glandular 
organs in plants as well as animals. Both Drosera and 
Dionea are excited by contact to pour out on to the surface 
Fic. 161.—ConN1Invity oF THE ProTorpiasm oF ConTiavous CELLS 
OF THE ENDOSPERM OF 4 Pat SEED (Bentinckia). Highly magnified. 
(After Gardiner.) 5 
a, contracted protoplasm of a cell; 6, a group of delicate proto- 
plasmic filaments passing through a pit in the cell-wall. 
of their leaves acid digestive secretions, which are the 
result of changes in the activity of the gland-cells. 
The conduction of the stimuli received is due in the 
higher animals to the existence of differentiated nerves. 
The way in which it ig carried out by plants has been much 
debated, but since the discovery of the continuity of the 
protoplasm through the cell-walls there is little doubt that 
we have here a similar mechanism. There is scarcely any 
differentiation, but the power of the protoplasm to con- 
duct disturbances from one part of the cell to another is a 
matter of common observation. The connecting strands 
between adjacent cells (fig. 161) will suffice to suggest how 
impulses from the tip of the root may reach the growing region. 
