180 Retrograde Varieties 



the form of the common beech-leaves. It is not 

 a bud-variation at all, and it is to be met with 

 quite commonly while the true reversions by 

 buds are very rare and are of the nature of 

 sports appearing suddenly and remaining con- 

 stant on the same twig. Analogous phenomena 

 of wide variability with true reversion may be 

 seen in the variety of the European hornbeam 

 called Carpinus Betulus heterophylla. The 

 leaves of this tree generally show the greatest 

 diversity in form. Some other cases have been 

 brought together by Darwin. In the first place 

 a subvariety of the weeping-willow with leaves 

 rolled up into a spiral coil. A tree of this kind 

 kept true for twenty-five years and then threw 

 out a single upright shoot bearing flat leaves. 

 The barberry (Berberis) offers another case; 

 it has a well known variety with seedless fruit, 

 which can be propagated by cuttings or layers, 

 but its runners are said always to revert to the 

 common form, and to produce ordinary berries 

 with seeds. Most of the cases referred to by 

 Darwin, however, seem to be doubtful and can- 

 not be considered as true proofs of atavism until 

 more is known about the circumstances under 

 which they were produced. 



Eed or brown-leaved varieties of trees and 

 shrubs also occasionally produce green-leaved 

 branches, and in this way revert to the type 



