492 CONCLUDING KEMAEKS. Chap. IX. 



injurious. A species which has ceased to be helio- 

 tropic might also be rendered apheliotropic by the 

 preservation of the individuals which teftded to cir- 

 cumnutate (though the cause of this and most other 

 variations is unknown) in a direction more or less 

 opposed to that whence the light proceeded. In like 

 manner a plant might be rendered diaheliotropic. 



