PLANT PHYSIOLOGY 



CHAPTER I 



INTRODUCTION 



All living beings are alike in kind, differing from one an- 

 other only in degree. To this conclusion scientific men have 

 been gradually driven back by the failure of every attempt 

 to discover and to define any fundamental difference between 

 animals and plants. The differences between the higher rep- 

 resentatives of the two so-called kingdoms— animal and veg- 

 etable—are so striking that no one can fail to see them. 

 Between the higher and the lower animal forms are differ- 

 ences as striking as those between higher animals and higher 

 plants. Between the higher and lower plant forms there are 

 similar differences. Likenesses always accompany these dif- 

 ferences. It is these likenesses which enable us to call a 

 given organism an animal or a plant. Between the higher 

 and lower members of the same kingdom, and between the 

 higher members of the two kingdoms, the differences are so 

 striking that the attention is almost wholly occupied with 

 them. It is natural that we should look more for differences 

 than for likenesses : for our ability to distinguish our friends 

 from our enemies, our own from our neighbor's possessions, 

 the Bird-foot Violet from the Swamp Violet, the dog from 

 the tree, is dependent upon our perception of differences 

 between them. It is necessary that we see differences : the 

 more intelligent the man, the keener is his perception of 

 differences; the higher the organism, the greater is its 

 difference from others. 



The study of low organisms reveals few differences. Suc- 

 cessfully to study such low organisms as the bacteria de- 



