VI PREFACE. 



years later a different arrangement was made ; the students 

 were required to perform the experiments for themselves, 

 and at the same time laboratory work in the chemistry of 

 metabolism was organised by Mr Acton. To enable the 

 students to carry out their work, written instructions 

 were needed, and the present book is the result of an 

 extension and elaboration of what we prepared for our 

 classes. 



The book makes no pretence to completeness, it 

 contains merely such a selection of experimental and 

 analytical work as seems suitable for botanical students. 



Part I, which deals with general physiology, is 

 necessarily of a somewhat more elementary character 

 than Part II, which treats a particular department of 

 physiology in a more special manner, and presupposes a 

 greater amount of knowledge on the part of the student. 



A few experiments which experience has shown to 

 be unsuitable have been omitted in the present edition. 

 The chief additions are: — Exps. 5 and 52 (Timiriazeff's 

 eudiometer), Exp. 83 (the importance of stomata in 

 gaseous interchange), Exps. 118 a, 118 b, 118 c (Stahl's 

 cobalt method), Exp. 205 A (Pfeffer and Czapek's method 

 of localising geotropic irritability in roots), Exp. 249 A 

 (chemotaxis in Bacteria), Exps. 249 B and c (chemotaxis 

 in pollen-tubes). 



