142 THE EVOLUTION THEORY 



other hand, in the weeping oak for instance, nearly all the seedlings 

 exhibit the character of the new variety, though ' in varying degrees.' 

 The records as to the transmissibility of bud- variations through seed 

 are probably not all to be relied upon, and new investigations are 

 much to be desired, but the fact that in many cases they may be 

 propagated not only by means of layers and cuttings but by seed 

 also, is most important in our present discussion, for it proves that 

 here too the varied determinants must be contained in a majority of 

 ids. As it is only a single shoot that exhibits the saltatory variation, 

 only the germ-plasm which was contained in the cells of this one 

 shoot can have varied, and it must have done so in so many ids that 

 the variation prevailed and found expression. But that, in this case 

 also, the variation does not appear in all, but only in a small majority 

 of ids, is proved by the frequent reversion of bud-varieties to the 

 ancestral form. I have already reported a case of this kind shown 

 to me by Professor Strasburger in the Botanic Gardens in Bonn, 

 where a hornbeam with deeply indented ' oak-leaves ' had one branch 

 which bore quite normal hornbeam leaves. In my own garden there 

 is an oak shrub of the 'fern-leaved' variety, whose branches bear 

 some leaves of the ordinary form ; variegated maples with almost 

 white leaves often exhibit in individual branches a reversion to the 

 fresh green leaves of the ancestral form. We see from this that what 

 is so energetically disputed by many must in reality occur — namely, 

 differential or non-equivalent nuclear division — for otherwise it would 

 be unintelligible how the ids of the new variety, if they once attain 

 a majority in the tree, could give place in an individual branch to 

 a majority of the ancestral ids. Only differential nuclear division, 

 in the manner of a reducing division, can be the cause of this. Of 

 course this implies only a dissimilar or differential distribution of the 

 ids between the two daughter-nuclei, not a splitting up of the indivi- 

 dual ids into non-equivalents. 



That in free Nature bud- variations left to themselves can ever 

 become permanent varieties is probably an unlikely assumption, 

 because of the inconstancy of their seeds which only breed true in 

 rare cases ; nor is it likely that such variations as the copper-beech, 

 the weeping ash, and so on could hold their own in the struggle for 

 existence with the older species; but there is certainly nothing 

 to prevent our assuming that, in certain circumstances, saltatory 

 variations, when they have a germinal origin, may become persistent 

 varieties and may even lead to a sjjlitting of the species. This may 

 happen, for instance, when the variations remain outside the limits 

 of good and bad, and thus are neither of advantage to the existence 



