THE NEEVOUS MECHANISM OF PLANTS 413 



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 

 Dioncea are excited by contact to pour out on to the surface 



FIG. 161, CONTINUITY OF THE PKOTOPLASM OF CONTIGUOUS CELLS 

 OF THE ENDOSPERM OF A PALM SEED (Bentinckia). Highly magnified. 

 (After Gardiner.) 



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 is 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. 



