xvi PLANTS IN RELATION TO MAN 331 



fully reduced to simple chemical and mechanical processes, this vital 

 force was derided and effaced from the list of natural agencies. 

 But by what name shall we now designate that force in nature which 

 is liable to perish whilst the protoplasm suffers no physical alteration 

 and in the absence of any extrinsic cause ; and which yet, so long 

 as it is not extinct, causes the protoplasm to move, to enclose itself, 

 to assimilate certain kinds of fresh matter coming within the sphere 

 of its activity and to reject others, and which when in full action 

 makes the protoplasm adapt its movements under external stimulation 

 to existing conditions in the manner which is most expedient? 



"This force in nature is not electricity nor magnetism ; it is not 

 identical with any other natural force ; for it manifests a series of 

 characteristic effects which differ from all other forms of energy. 

 Therefore, I do not hesitate again to designate as ' vital force ' this 

 natural agency, not to be identified with any other, whose immediate 

 instrument is the protoplasm, and whose peculiar effects we call life. 

 The atoms and molecules of protoplasm only fulfil the functions 

 which constitute life so long as they are swayed by this vital force. 

 If its dominion ceases they yield to the operation of other forces. 

 The recognition of a special natural force of this kind is not in- 

 consistent with the fact that living bodies may at the same time be 

 subject to other natural forces" (vol. i. p. 52). 



And again, after discussing the various effects produced 

 by that wonderful substance chlorophyll, he says : 



"We see the effective apparatus, we recognise the food-gases 

 and food-salts collected for working up, we know that the sun's rays 

 act as the motive force, and we also identify the products which 

 appear completed in the chlorophyll granules. By careful com- 

 parison of various cells containing chlorophyll, having found by 

 experience that under certain external conditions the whole apparatus 

 becomes disintegrated and destroyed, it is indeed permissible to 

 hazard a conclusion about the propelling forces. But what is 

 altogether puzzling is, how the active forces work, how the sun's rays 

 are able to bring it about that the atoms of the raw material abandon 

 their previous grouping, become displaced, intermix one with another, 

 and shortly reappear in stable combinations under a wholly different 

 arrangement. It is the more difficult to gain a clear idea of these 

 processes, because it is not a question of that displacement of the 

 atoms called decomposition, but of that process which is known as 

 combination or synthesis'''' (vol. i. p. 377). 



I have made these quotations from one of the greatest 

 German writers on botany in order to show that a professor 

 of the science, with a most extensive knowledge of every 

 aspect of plant -life, supports the conclusion I had already 



