68 HOLISM AND EVOLUTION chap. 



means and does much more than the physical or chemical 

 details which we can identify. Not only is there control and 

 organisation of these details, but the physico-chemical 

 agencies themselves are of a new type. For instance, 

 oxygen and carbon dioxide appear to be taken in through the 

 stomata of the leaves, but this is not merely a case of ordi- 

 nary osmosis. Again, liquid materials in the form of dis- 

 solved salts or other inorganic substances are taken in 

 through the roots, but this also is not a case of ordinary phys- 

 ical osmosis. Again, these liquids rise in the plant cells as if 

 it were merely a case of surface tension or capillary action. 

 But as a matter of fact these are all cases of metabolism in 

 which subtle changes take place in the protoplasm, changes 

 whose details are no doubt apparently all of a physico-chem- 

 ical character, but whose distinctive character lies not only 

 in these details but in the new system of control in which 

 they are organised and regulated. The theory which has 

 been developed to account for the physico-chemical reactions 

 which take place in all organic change and functioning is 

 based on the assumption of very complex substances of the 

 nature of ferments or enzymes being formed and acting in 

 the protoplasm. It is, for instance, through the agency of 

 the enzymes in the protoplasm that all the secretions are 

 formed which build up the different parts of the plant. 

 Thus also the transformation of the carbon dioxide in the 

 green cells of the leaves into starch is not a chemical change 

 of the ordinary type, but is effected in the presence of 

 colloidal catalysts like chlorophyll and other enzymes, at 

 whose surfaces sunlight can transform the carbon dioxide 

 so as to form successively formaldehyde, dextrose, maltose, 

 and finally soluble and insoluble starch. Mere physical 

 and chemical reactions have been identified. But it is quite 

 possible that there is much more, and that the organic 

 process behind them is much more complicated and 

 characteristic. Again, both respiration and metabolism 

 are processes effected through enzyme action at colloid 

 surfaces instead of being of the ordinary mechanical char- 

 acter. The enzymes are thus conceived as being cat- 



