LIFE AND DEATH. 279 



and the same plant must have all these elements, 

 the atom groupings and modes of building up 

 and breaking down may be very different in 

 each case. 



Again, the cell-protoplasm, bathed by the sap 

 taken in by roots from the soil or fed directly by 

 that derived from the leaves, must be exposed to 

 very different stimuli and modes of nourishment, 

 etc., from those incurred by the protoplasm of 

 the nucleus which it encloses : and similar con- 

 clusions must apply in turn to the protoplasm 

 of the root in the dark moist soil and of the 

 leaf in the light dry air, or to that of the super- 

 ficial epidermis cells as contrasted with that of 

 the deeply immersed pith, and so on. 



It is no doubt in these directions that we must 

 seek for the explanation of many life-phenomena 

 at present quite beyond explanation. Thus, it is 

 tolerably easy to modify the action of the cell- 

 protoplasm of a plant, by exposing it to differences 

 of illumination, temperature, moisture, and so forth, 

 within certain limits ; at least, since the changes in 

 stature, tissue differentiation, cell-secretions, flower- 

 ing capacity, etc., of plants affected by such factors 

 of the environment e.g. alpine plants brought into 

 the plains must be due to changes in the mode of 

 activity of the protoplasm, we must assume that 

 the above factors affect the latter. But it is ex- 

 tremely difficult to reach the nuclear-protoplasm 

 directly by such stimuli, as proved by the experi- 

 ence that even where we allow the factors to act 

 for a long time, no permanent change can be 



