146 CORKELATED VARIATION. Chap. V. 



t:\in varieties are said to withstand certain climates better than 

 others ; this is verv strikingly shown in works on fruit-trees 

 published in the United States, in which certain varieties are 

 liabituallj recommended for the Northern and others for the 

 Southern States ; and, as most of these vari(>tics arc of recent 

 origin, they cannot owe their constitutional differences to hab- 

 it. The case of the Jerusalem artichoke, which is never propa- 

 gated in England by seed, and of which consequently new va- 

 rieties have not been produced, has even been advanced — for 

 it is now as tender as ever it was — as proving that acclimatiza- 

 tion cannot be effected ! Tlie case, also, of the kidney-bean 

 has been often cited for a similar purpose, and with much 

 greater weight; but until some one will sow, during a score of 

 generations, his kidney-beans so early that a very large pro- 

 portion 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 precau- 

 tions, the experiment cannot be said to have been tried. Nor 

 let it be supposed that differences in the constitution of seed- 

 ling kidney-beans never appear, for an account has been pub- 

 lished how much more hardy some seedlings were than others; 

 and of this fact I have myself observed striking instances. 



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

 and disuse, have, in some cases, played a considerable part in 

 the modification of the constitution, and of the structure of 

 various organs ; but that the effects of use and disuse have 

 often been largely combined with, and sometimes overmastered 

 by, the natural selection of innate variations. 



Correlated 'Variation. 



I mean by this expression that the whole organization is so 

 tied together during its growth and development, that when 

 slight variations in any one part occur, and are accumulated 

 through natural selection, other parts become modified. This 

 is a very important subject, most imperfectly understood, and 

 no doubt totally different classes of facts may be here easily 

 confounded together : we shall presently see that simple in- 

 heritance often gives the false appearance of correlation. The 

 most obvious instance of real correlation is, that variations of 

 structure arising in the young or in the larvae naturally tend 

 to affect the structin-e of the mature animal ; in the same man- 

 ner as ;my malconfonnation in the early embryo is knoAvn 



