216 LIVING PLANTS 



the limits of animal and plant life, after care- 

 fully reviewing the whole subject, sa3's in his 

 concluding sentence that "a fast and abso- 

 lute boundar^^ between animals and plants 

 does not exist." The last sentence of Profes- 

 sor Huxley's lecture, delivered in London in 

 1876 upon the border territory between the 

 animal and the vegetable kingdoms, breathes 

 the same sentiment. It was his opinion that 

 "the difference between animal and plant is 

 one of degree rather than of kind, and that 

 the problem whether, in a given case, an 

 organism is an animal or a plant, may be 

 essentially insoluble." 



The positive statements of such leaders of 



thought require no additional evidence to 



show that finding crucial tests to apply 



under all circumstances is well nigh hopeless. 



And yet the writer believes that the last word 



is not said, and that a clue will yet be found 



leading to a reasonably clear solution of the 



problem. 



Characters It has long been recognized that characters 



from structure drawn from structure are far more reliable in 



and function determining relationship than characters 



drawn from function. The latter respond 



more readih^ to changes in the environment, 



and therefore forms having little affinity may 



possess the same physiological adaptations. 



