vi VEGETABLE PHYSIOLOGY 



With this view I have endeavoured to present the 

 plant as a living organism, endowed with particular 

 properties and powers, realising certain needs, and meet- 

 ing definite dangers. I have attempted to show it to be 

 properly equipped to encounter such adverse conditions, 

 and to avail itself of all the advantages presented to it by 

 its environment. 



I have also set before myself another purpose, which, 

 however, is naturally subordinate to the one just mentioned. 

 When we consider the origin of the different organisms 

 which we find around us, we are led irresistibly to the 

 conclusion that the classification of living beings into 

 animals and plants has been too strongly insisted upon in 

 the past, and that while much has been made of their differ- 

 ences, their points of resemblance have been minimised, 

 The fact that organisms exist, which it is difficult or 

 impossible to refer with certainty to either kingdom, points 

 to a fundamental unity of living substance. Protoplasm 

 in short is the same material, whether we call it animal or 

 vegetable. This being the case, its conditions of life and its 

 immediate necessities must be practically the same, what- 

 ever its degree of differentiation in either direction. I 

 have tried to bring out this identity of living substance 

 throughout the book, and to indicate that apparent differ- 

 ences of behaviour and structural arrangement are to be 

 traced rather to differences of environment and habit of 

 life than to those of constitution. The correspondence of 

 the processes of respiration in animals and plants has long 

 been recognised ; many points of similarity in those of 

 nutrition have been observed. The idea is, however, still 

 prevalent that plants live upon inorganic materials ab- 

 sorbed from the air and from the soil. This seems to 

 indicate a fundamental difference between the modes of 

 nutrition of animal and vegetable protoplasm. I have 



