CHAPTER XXXVII 



GENERAL REVIEW 



The different chapters of this book describe and discuss 

 observations on the movements of growing organs under 

 the changing conditions of the environment. Some of 

 these, such as variation of temperature and the alternation 

 of light and darkness, affect the rate of growth ; others, 

 such as the action of gravity, of unilateral illumination, and 

 of contact with foreign bodies, induce changes in the direction 

 of growth, these changes being generally described as 

 Tropisms. They are of many kinds and are more or less 

 complex, so that it is no easy matter to analyse them in 

 the hope of arriving at some general principles which would 

 explain them all. 



The attempt has been made to account for the 

 movements teleologically, to regard them as determined 

 by the advantage they may contribute to the well-being 

 of the plant, rather than to study them physiologically as 

 manifestations of stimulation and response. It is the latter 

 experimental method which has been pursued in the work 

 here recorded, with results summarised in this chapter. 



All movements of growing organs, whether spontaneous 

 or induced, are effected by change in the rate of growth ; 

 this change is subject to modification according to the 

 vigorous or feeble tonic condition of the growing organ. It 

 is therefore necessary to have means of immediate measure- 

 ment of the actual rate of growth and its induced variation. 



The Method of Magnified Record 



The High Magnificatioii Cresco graph permits of the deter- 

 mination of the absolute rate of grow^th and its induced 



