PREFACE TO THE FIRST EDITION 



THE following work is not intended as a text-book for beginners, but 

 as a hand-book containing a complete account of the present state of our 

 knowledge concerning the general processes of metabolism and the sources 

 of energy in the plant. Consequently an acquaintance with the principles 

 of anatomy, morphology and physiology, as well as of physics and chemistry, 

 will be assumed on the part of the reader. 



The older literature has been referred to only when it forms the basis 

 of our present knowledge. In many places, however, reference has been 

 made to works containing ideas which are now of merely historical interest. 

 Wherever the original literature has been unattainable, the sources of 

 information made use of have been mentioned. In the catalogue of scientific 

 papers, published by the Royal Society of London, a complete account is 

 given of all the existing abstracts, translations, &c. that have been made of 

 each paper, and by referring to this source the reader can decide whether 

 any other source will be more accessible to him than the one quoted by me. 

 It has not been my purpose to furnish a mere collection of the conclusions 

 and results recorded in these different original publications. On the contrary 

 I have attempted throughout to view the whole critically, and to indicate 

 what facts may be regarded as'defkiitdy^stablished, as well as to point out 

 where only insufficient and incomplete observations are presented to us. 

 If an impulse is thus given to further research, broadening and increasing 

 our knowledge, this book will have fulfilled its most important purpose. 

 Knowing, as I do, its inevitable imperfections and incompleteness, I cannot 

 send it forth with the feeling that all that was originally intended has been 

 accomplished. Two courses only were open to me either to issue the 

 work as it now stands, and to prepare for a more complete critical account 

 by further research, or to regard the results of many years' labour as studies 

 undertaken for my own instruction, and make no further use of them. 



W. PFEFFER. 



TUBINGEN, December 18, 1880. 



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