104 LUTHER BURBANK 



period at which its immediate ancestors had been 

 accustomed to assume a condition of dormancy. 



How is our theme of the power of instinctive 

 habit to be made to coincide with this seemingly 

 illogical departure? 



Our answer is found, as it has been found 

 in the explanation of other anomalies of plant 

 development, in an appeal from the immediate 

 ancestry of the rhubarb to the countless galaxies 

 of its vastly remote ancestry. 



In point of fact the rhubarb is, in all prob- 

 ability, a tropical plant that has but recently 

 migrated to temperate zones using the word 

 recently in the rather wide sense necessary when 

 we are dealing with questions of racial develop- 

 ment under natural conditions. In other words, 

 it is perhaps only a matter of a few hundred 

 generations since all the ancestors of the existing 

 rhubarb tribes were growing in a tropical tem- 

 perature, and hence, like the tropical plants in 

 general, were all-the-year bearers. 



In more recent generations, this habit of per- 

 petual bearing has been modified, in case of the 

 rhubarb as in the case of nearly all plants of 

 temperate zones, to meet the altered condi- 

 tions of a climate in which seasons change. 



To adapt themselves to this change of climate, 

 plants were obliged to go into retirement in the 



