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 retrogression is every- 

 where so active that it can almost be said to be 

 the prevailing movement. Reduction in the veg- 

 etative and generative organs, in the anatomical 

 structure and growth of the stems, and in sun- 

 dry other ways is the method by which the 

 monocotyledons have originated as a group 

 from their supposed ancestors among the lower 

 dicotyledonous families. Retrogression is the 

 leading idea in the larger families of the group, 



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