Heredity and Natural Selection. 291 



maturely on some striking case of biid-yariation — for in- 

 stance, 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 under 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 under the widely different 

 climate of Virginia, produces a single bud, and this 

 yields a branch which ever after bears nectarines. . . . 

 Now is it possible to conceive of conditions more exactly 

 alike than these 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 ap- 

 parent 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-varia- 

 tion, nectarines; the nectarines thus produced, no doubt 

 differ a little from each other, but still they are necta- 

 rines. 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 rela- 

 tion to any particular variation, in comparison with the 

 organization or constitution of the being which varies. 

 We are thus driven to conclude that in most cases the 

 conditions of life play a subordinate part in causing any 

 particular modification; like that which a spjirk plays, 

 when a mass of combustibles bursts into flame, the 

 nature of the flame depending on the combustible mat- 

 ter and not on the spark. . . . Hence, although it must 



