LECTURE XXII 



SYSTEMATIC ATAVISM 



The steady cooperation of progression and re- 

 trogression is one of the important principles 

 of organic evolution. I have dwelt upon this 

 point more than once in previous lectures. I 

 have tried to show that both in the more im- 

 portant lines of the general pedigree of the 

 vegetable kingdom, and in the numerous lateral 

 branches ending in the genera and species with- 

 in the families, progression and retrogression 

 are nearly always at work together. Your at- 

 tention has been directed to the monocotyledons 

 as an example, where regression is everywhere 

 so active that it can almost be said to be the pre- 

 vailing movement. Eeduction in the vegetative 

 and generative organs, in the anatomical struc- 

 ture and growth of the stems, and in sundry 

 other ways is the method by which the mono- 

 cotyledons as a group have originated from 

 their supposed ancestors among the lower di- 

 cotyledonous families. Retrogression is the 

 leading idea in the larger families of the group, 



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