vi INTRODUCTION 



further study and practical experience. The writer of 

 an elementary book must always adopt short views and 

 make dogmatic statements which he knows to be no 

 more than approximations to the truth. I can only hope 

 that the constant reference to experiment, and the whole 

 style in which the book has been written, will keep 

 before the reader an appreciation of how much still 

 remains unsaid. 



Even more than for the student, this book is intended 

 for the workaday farmer who wants to get an intelli- 

 gent conception of how his crops and stock make their 

 growth. Complex and unknown as many of these 

 processes are, the main outlines are sufficiently estab- 

 lished to have a bearing upon practice ; but the practical 

 application can be more surely and readily made if the 

 farmer, with his inside knowledge of the way things can 

 be done, will learn the theory, than by any attempt of the 

 scientific man striving from the outside to get up the 

 working conditions. 



Moreover, the subject is interesting ; it should neither 

 be difficult nor tedious for the man with an ordinary 

 education to learn how a plant draws its nutriment 

 from the soil, and how the animal depends in its turn 

 upon the plant ; so if this book is not readable, mine is 

 the fault, and I have failed in the object with which I 

 set out. To this end I have avoided technical language 

 as much as possible, and I have assumed that the reader 

 possesses little or no knowledge of chemistry. Of 

 course, a book of this kind cannot be finally intelligible 

 unless the reader possesses some ideas about the con- 

 stitution of air and water and the nature of chemical 



