PARTHENOGENETIC PURE LINE OF APHIS AVEN^ FAB. 1 05 



isolation 1 1. Notwithstanding the selection made in this subline 

 we find the typical unimodal frequency polygon (shown by the 

 heavy unbrokem line) representing the normal variations of 

 a fluctuating character. 



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FIG. 17. Frequency polygon to show variations in body length for the 

 individuals obtained in isolation No. n. The polygon is broken up into three com- 

 ponents representing the frequency polygons for the first score, second score, and 

 last four generations of this isolation. For further explanation see text. 



The causes for the variation in fluctuations have not been well 

 understood in most instances. De Vries maintains that in plants 

 they depend probably exclusively upon nutrition. I find that 



