Chap. XXII. CAUSES OF VARIABILITY. 255 



of a id oss-rose on a Provence-rose is a return to a former state 

 for mossiness of the calyx lias been observed in no natural 

 species; the same argument is applicable to variegated and 

 laciniated leaves; nor can the appearance of nectarines on 

 peach-trees be accounted for with any probability on the 

 principle of reversion. But bud-variations more immediately 

 concern us, as they occur far more frequently on plants which 

 have been highly cultivated during a length of time, than 

 on other and less highly cultivated plants ; and very few well- 

 marked instances have been observed with plants growing 

 under strictly natural conditions. I have given one instance of 

 an ash-tree growing in a gentleman's pleasure-grounds; and 

 occasionally there may be seen, on beach and other trees, twigs 

 leafing at a different period from the other branches. But our 

 forest trees in England can hardly be considered as living under 

 strictly natural conditions; the seedlings are raised and pro- 

 tected in nursery-grounds, and must often be transplanted into 

 places where wild trees of the kind would not naturally grow. 

 It would be esteemed a prodigy if a dog-rose growing in a hedge 

 produced by bud-variation a moss-rose, or a wild bullace or 

 wild cherry-tree yielded a branch bearing fruit of a different 

 shape and colour from the ordinary fruit. The prodigy would 

 be enhanced if these varying branches were found capable of 

 propagation, not only by grafts, but sometimes by seed; yet 

 analogous cases have occurred with many of our highly culti- 

 vated trees and herbs. 



These several considerations alone render it probable that 

 variability of every kind is directly or indirectly caused by 

 changed conditions of life. Or, to put the case under another 

 point of view, if it were possible to expose all the individuals 

 of a species during many generations to absolutely uniform 

 conditions of life, there would be no variability. 



On the Nature of the Changes in the Conditions of Life which 



induce variability. 



From a remote period to the present day, under climates and 

 circumstances as different as it is possible to conceive, organic 

 beings of all kinds, when domesticated or cultivated, have varied. 



