104 LLTlfl n BURB. 



\ N I\ 



perkxi at which its imtnediate ancestors had been 

 accustomed to assume m condition of dormancy. 



How is otir theme of the power of instinctive 

 habit to be made to coincide with this seemingly 

 illogical departure? 



Our answer is found, as it ha^ been found 

 in the explanation of other aiumudies of plant 

 development, in an appeal from the immediate 

 ancestr}' 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 tones — using tlie 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 

 gmerations 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 



