Preface vii 



tive influences. But adaptation seems to me to guide the course 

 of a mightier current upon which mechanical causation and other 

 influences are ripples or eddies, or at least no more than the waves 

 whose only lasting influence is occasionally to open new directions 

 for the current to move in. With this belief in adaptation, I have 

 naturally not hesitated to use the corresponding language of 

 purpose, not a mystical, supernatural, forethoughtful purpose, 

 but a physical, natural, experiential purpose, which does not 

 presuppose any forethought, but only the preservation and 

 accumulation of the results of past experiences wherein each step 

 in advance was purely chanceful, and survived only because it 

 happened to fit. 



There is one other matter of this kind I would mention, and 

 that will be all. Throughout the book I have made great use of 

 diagrams, generalizations, and conventionalizations; and this may 

 seem inconsistent with the vitalistic rather than mechanistic tone 

 of the work. The scientific and educational status of this practice 

 are sufficiently explained in Chapter I, but I would like also to 

 say that I think our advance in plant physiology is measured 

 exactly by our ability to represent each detail in a mechanical 

 diagram, a physical formula, or a chemical equation. For the 

 evidence certainly indicates that every individual process of 

 plants is purely mechanical, physical, or chemical. What cannot 

 thus be explained, and what we have made as yet little progress 

 towards explaining, is the nature of the influence which establishes 

 and holds these processes in orderly sequences repeated in wonder- 

 fully complicated cycles generation after generation. When we 

 have explained the operation of each gun, and dynamo, and 

 powder-hoist on a battleship, have we thereby explained the 

 rationale of the operation of a battleship? Here is where the real 

 difference lies today between mechanism and vitalism. And this 

 is the vitalism of this book, not a supernatural vitalism of the 

 theological type, and certainly not designed for theological needs, 

 but a perfectly natural vitalism based on the superior interpretive 



