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CHAPTEK XVIII 



THE ENERGY OF THE PLANT 



The various operations which we have seen to be con- 

 tinually going on in the body of the plant involve the execu- 

 tion of a considerable amount of work. This is very evident 

 when we observe only the enormous development of a 

 large tree, and compare it with the relatively small seed 

 from which it has sprung. Such a process of construction 

 has involved the preparation of a vast quantity of highly 

 complex material from very simple chemical substances. 

 The processes incident to life also, though they may not 

 lead directly to the formation of such substances, cannot 

 be conducted without involving a considerable amount of 

 work, whether the plant is a minute body consisting of a 

 single protoplast, or an organism of a much higher degree 

 of complexity. 



We must therefore turn our attention to the question of 

 the supply and utilisation of the energy at the expense of 

 which the various processes of life are carried out. At the 

 outset it will be well to consider what demands for energy 

 we find presented by the plant, or what are the ways in 

 which energy is expended or lost. 



Some of these have been incidentally alluded to in the 

 preceding chapters, though we have not specially regarded 

 them from this point of view. We may refer especially to 

 the very great evaporation of water from the living cells 

 into the intercellular spaces, which we have seen is in some 

 cases supplemented by an evaporation from the general 

 external surface, when this is not covered by any very 



