404 VEGETABLE PHYSIOLOGY 



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. 163) will suffice to suggest how 

 impulses from the tip of the root may reach the growing 



cells. 



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 plajat which in its elaboration or in its peculiar 



FIG. 163. CONTINUITY OF THE PROTOPLASM OF CONTIGUOUS CELLS 

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

 magnified. (After Gardiner.) 



ft, contracted protoplasm of a cell ; b, a group of delicate proto- 

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



efficiency can be compared with the co-ordinating mechanism 

 of animals. Certain responses to stimulation can be effected, 

 but no definite regulation of any function shows any great 

 completeness. We have seen this particularly in the case 

 of the influence of temperature. Though a certain range 

 of temperature is imperative for the plant's well-being, it 

 has no power, or but little, to co-ordinate its own produc- 

 tion or expenditure of heat with the variations of tempera- 

 ture to which it is exposed. 



Neither anatomically nor physiologically do we find 

 much differentiation in the direction of such co-ordination. 

 The plant shows an almost complete absence of the 



