THE METABOLISM OF PLANTS. 325 



leaf: Burdon-Sanderson regards it as "a visible sign of an 

 unknown molecular process/' which he considers to be "an 

 explosive molecular change," and as of the same nature as 

 the negative variation which follows upon the stimulation 

 of muscles and nerves. 



The stimulation of the leaf of Dionaea may or may not be 

 followed by the closing of the leaf, but in either case the 

 electrical phenomena above described are manifested. This 

 shews that the electrical changes observed in connexion with 

 the stimulation of motile organs are not due to movement of 

 the organs, but are the expression of preliminary changes 

 taking place in their cells. 



Summing up the evidence which is now before us we come 

 to the following conclusions: (i) that the so-called "normal" 

 currents (including Ranke's " true " and " false " currents) are 

 not the expressions of a dissipation of the energy of the plant; 

 (2) that the electrical disturbances exhibited by motile organs 

 on stimulation, or at least the negative variation, are the ex- 

 pression of the dissipation of a portion of the energy set free 

 as the result of molecular change in the protoplasm. 



We have now concluded our study of the metabolism of 

 plants, and it only remains for us to bring together the most 

 important points. The best means of stating them clearly 

 will be to draw up an account of the income and expenditure 

 of a plant. 



In the case of a plant possessing chlorophyll, the income 

 of matter consists, as we have seen, of the food (salts, water, 

 carbon dioxide, free oxygen), and the income of energy 

 of kinetic energy in the form of light and heat, the former 

 being the more important of the two items. The great bulk 

 of the food absorbed is converted into organic matter, which 

 is retained by the plant in the form of organised structures, 

 of reserve-materials, and of waste-products which are not ex- 

 creted. At the same time a loss of matter, in the form of the 



