teXPERIMENTAL EVOLUTION 



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Fig. S4- — Curves of variation, illustrating the diflference between 

 fluctuation about a given mean, and the appearance of a new mean, i.e., 

 mutation. At the right, variations in the stature of Oenothera Lamarchiana; 

 at the left, variation in the stature of Oenothera nanella, a form derived 

 from 0. Lamarchiana by mutation. (After de Vries.) 



l?j(;_ 55.— Leaves of varieties of the Boston fern {N ephrolepis) , showing 

 (from left to right) progressive branching of the pinns and pinnules, and 

 illustrating so-called " orthogenetic saltation." (After R. C. Benedict.) 



