288 



DEFINITE ACTION OF THE 



Chap. XXIII. 



tion had been definitely caused by some change in the conditions 

 to which the plants had been exposed ; yet, in other cases, such 

 an admission is extremely difficult. As new characters some- 

 times appear by bud-variation, which do not occur in the parent- 

 species or in any allied species, we may reject, at least in these 

 cases, the idea that they are due to reversion. Now it is well 

 worth while to reflect maturely on some striking" case of bud- 

 variation, for instance that of the peach. This tree has been 

 cultivated by the million in various parts of the world, has been 

 treated differently, grown on its own roots and grafted on various 

 stocks, planted as a standard, against a wall, and nncler glass ; 

 yet each bud of each sub-variety keeps true to its kind. But 

 occasionally, at long intervals of time, a "tree in England, or 

 nnder the widely-different climate of Virginia, produces a single 

 bud, and this yields a branch which ever afterwards bears nec- 

 tarines. Nectarines differ, as every one knows, from peaches 

 in their smoothness, size, and flavour ; and the difference is so 

 great, that some botanists have maintained that they are speci- 

 fically distinct. So permanent are the characters thus suddenly 

 acquired, that a nectarine produced by bud-variation has pro- 

 pagated itself by seed. To guard against the supposition that 

 there is some fundamental distinction between bud and seminal 

 variation, it is well to bear in mind that nectarines have like- 

 wise been produced from the stone of the peach ; and, reversely, 

 peaches from the stone of the nectarine. Now is it possible to 

 conceive external conditions more closely alike than those to 

 which the buds on the same tree are exposed? Yet one bud 

 alone, out of the many thousands borne by the same tree, has 

 suddenly without any apparent cause produced a nectarine. But 

 the case is even stronger than this, for the same flower-bud 

 has yielded a fruit, one-half or one-quarter a nectarine, and 

 the other half or three-quarters a peach. Again, seven or eight 

 varieties of the peach have yielded by bud-variation nectarines : 

 the nectarines thus produced, no doubt, differ a little from 

 each other; but still they are nectarines. Of course there 

 must be some cause, internal or external, to excite the peach- 

 bud to change its nature ; but I cannot imagine a class of facts 

 better adapted to force on our minds the conviction that what 

 we call the external conditions of life are quite insignificant in. 





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