CHAPTER XXX. 



LIFE AND DEATH. 



Protoplasm Hypothesis as to its stt-itcture atid be- 

 haviour Assimilation Growth Respiration 

 Metabolism Action of the environment Nuclear 

 protoplasm Pollination Grafting Parasitism 

 Graft-hybrids Life Death Variation Disease. 



We have seen that all the essential phenomena 

 of disease concern only the living substance 

 the protoplasm of the plant, and that how- 

 ever complex the symptoms of disease may be, 

 the occurrence of discolorations, lesions, hyper- 

 trophies, and so forth are all secondary matters 

 subsidiary to the fundamental alterations of 

 structure and function constituting the disease. 

 It remains to see if we can adopt any hypothesis 

 as to the nature of this physical basis of life the 

 protoplasm which shall help us to understand 

 still more clearly in what must reside those 

 processes which, so long as they proceed har- 

 moniously and uninterruptedl}^, constitute life and 



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