SOME EXPERIMENTS OF LUTHER BUR BANK. 205 



"On the average, perhaps about six generations fairly fix a varia- 

 tion, but this varies greatly, depending upon previously acquired 

 hereditary tendencies. Bringing a species into a new environment dis- 



Leaves showing a Numbbb of Strawberry-Raspberry Hybrids and a Cluster of 



the Blossoms. 



turbs its fixity. Rich soil especially gives rise to variations in growth 

 which seem to be new, and by repetition become inherently fixed. 

 Sometimes ancestral states are brought about by good soil; sometimes 



