404 VEGETABLE PHYSIOLOGY 



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 

 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 



FIG. 161. CONTINUITY OF THE PROTOPLASM OP CONTIGUOUS CELLS 

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

 magnified. (After Gardiner.) 



a, contracted protoplasm of a cell ; &j a group of delicate proto- 

 plasmic filaments passing through a pit in the cell-wall. 



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. 



The co-ordination of these factors we have seen is one 

 of the most marked features of a highly differentiated 

 nervous system. In this respect we cannot note anything 

 in the plant which in its elaboration or in its peculiar 

 efficiency can be compared with the co-ordinating mechanism 

 of animals. Certain responses to stimulation can be effected, 



