Chap, v.] CORRELATED VARIATION. 177 



of the Jerusalem artichoke, which is never propagated 

 in England by seed, and of which consequently new 

 varieties have not been produced, has even been ad- 

 vanced, as proving that acclimatisation cannot be ef- 

 fected, for it is now as tender as ever it was! The case, 

 also, of the kidney-bean has been often cited for a 

 similar purpose, and with much greater weight; but 

 until someone will sow, during a score of generations, 

 his kidney-beans so early that a very large proportion 

 are destroyed by frost, and then collect seed from the 

 few survivors, with care to prevent accidental crosses, 

 and then again get seed from these seedlings, with the 

 same precautions, the experiment cannot be said to have 

 been tried. Nor let it be supposed that differences in 

 the constitution of seedling kidney-beans never appear, 

 for an account has been published how much more 

 hardy some seedlings are than others; and of this fact 

 I have myself observed striking instances. 



On the whole, we may conclude that habit, or use 

 and disuse, have, in some eases, played a considerable 

 part in the modification of the constitution and struc- 

 ture; but that the effects have often been largely com- 

 bined with, and sometimes overmastered by, the natural 

 selection of innate variations. 



Correlated Variation. 

 I mean by this expression that the whole organisa- 

 tion is so tied together during its growth and develop- 

 ment, that when slight variations in any one part occur, 

 and are accumulated through natural selection, other 

 parts become modified. This is a very important sub- 

 ject, most imperfectly understood, and no doubt wholly 

 different classes of facts may be here easily confounded 



