404 VEGETABLE PHYSIOLOGY 
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 
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 
Fic. 161—ConTinuity oF THE PROTOPLASM OF CONTIGUOUS CELLS 
or THE ENDospERM oF A Patm SEED (Bentinckia). Highly 
magnified. (After Gardiner.) 
a, contracted protoplasm of a cell; b, 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 theco-ordinating mechanism 
of animals. Certain responses to stimulation can be effected, 
