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CHAPTEE XXIII 



THE PKOPEKTIES OF VEGETABLE PROTOPLASM 



THE influence of the environment upon the structure of 

 plants we have seen to be far-reaching. Different condi- 

 tions of the surroundings are followed by differences of 

 structure which are greater in proportion as the time 

 during which those conditions act is more and more pro- 

 longed. The living substance of the plant is clearly the part 

 influenced by the environment, for we have seen that the 

 skeleton and other non-living parts of the plant owe their 

 construction to its activity. We may therefore with advan- 

 tage pause at this point to examine a little more closely 

 the properties which are exhibited by vegetable proto- 

 plasm. 



We have seen throughout all the foregoing chapters 

 that all the processes which conduce to the well-being of 

 the plant are, to a large extent, if not entirely, under the 

 control of the living substance. Though the absorption 

 of its food materials from the air and the soil is due to 

 physical processes, these are nevertheless largely regulated 

 by the behaviour of the protoplasm under all sorts of vary- 

 ing conditions. The manufacture of food from these crude 

 materials, and its subsequent distribution, the accumula- 

 tion and dissipation of energy, the processes of nutrition 

 and growth, are all subject to the same regulation. 



But there are also other properties of protoplasm which 

 have not so far been more than incidentally referred 

 to. The plant exhibits particularly the power of appre- 

 ciating changes in its surroundings, and is capable of 

 adapting itself in various ways to such changed conditions. 



