98 LUTHER BURBANK 



determined by "instinct," which after all sug- 

 gests only the spontaneous response to environ- 

 ing conditions, present or reflected through 

 heredity. 



And the force of the various instincts or habits, 

 in the case of a plant, as in the case of birds and 

 animals, is overwhelmingly powerful and quite 

 beyond the possibility of change in any given 

 generation. 



To cite a single illustration from the case in 

 hand, every gardener knows that he cannot by 

 any process of cultivation make the ordinary 

 rhubarb plant change its fixed habit of spring 

 production. No amount of coaxing and no man- 

 ner of soil cultivation or fertilization can take 

 from the rhubarb the impelling force of the 

 hereditary tendency to put forth its stalks in 

 the spring time rather than in summer or fall 

 or winter. 



And a similar fixity of habit characterizes, in 

 greater or less measure, most other familiar 

 cultivated plants. Artificial selection has ex- 

 tended the season in certain cases, and early or 

 late-bearing varieties have been developed as 

 already noted; but for each variety the habit of 

 producing at a given time of year is one of the 

 most fixed and as regards any given genera- 

 tion unalterable of tendencies. 



