242 CAUSES OF VARIABILITY. Chap. XXIJ. 



doubted wlietlier the variations of this, the least valuable of 

 all our cereals, have been closely observed. 



Bud- variation, which was fully discussed in a former chap- 

 ter, shows us that variability may be quite independent of 

 seminal reproduction, and likewise of reversion to long-lost 

 ancestral characters. No one will maintain that the sudden 

 appearance of a moss-rose on a Provence-rose is a return to a 

 former state, for mossiness of the calyx has been observed in 

 no natural species ; the same argument is applicable to varie- 

 gated and laciniated leaves ; nor can the appearance of necta- 

 rines on peach-trees be accounted for on the principle of rever- 

 sion. 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 beech and other trees, 

 twigs leahng 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 protected 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 cherrj'-tree jdelded a branch 

 bearing fruit of a different shape and colour from the ordinar}'- 

 fruit. The prodigy would be enhanced if these varying 

 branches were found capable of propagation, not only by 

 grafts, but sometimes bj^ seed ; yet analogous cases have 

 occurred with many of our highly cultivated 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. 



