THE WINTER RHUBARB 



development, in an appeal from the immediate 

 ancestry of the rhubarb to the countless galaxies 

 of its vastly remote ancestry. We have already 

 pointed out that all plant life traces back its origin, 

 if you go far enough, to the luxuriant tropical 

 vegetation of the Carboniferous Era. 



But in the case of the rhubarb it is not 

 necessary to go back so far as this to find an 

 ancestry habituated to tropical conditions. 



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 the tropics, and 

 hence, like 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 case of nearly all plants of tem- 

 perate zones, to meet the altered conditions of a 

 climate in which summer and winter alternate. 



To adapt themselves to this change of climate, 

 plants were obliged to go into retirement in the 

 winter season, and natural selection preserved 



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