92 ACQUIRED CHARACTERS sec. 



the first offspring of tlie individuals which have betaken 

 themselves to caves are born with liizht skins and are no 

 longer exposed to the action of light, the later descendants 

 will very soon remain jDcrmanently light coloured. 



Further, liow immense is the direct effect of warmth on 

 the vegetable world, and how obvious the inheritance of this 

 effect. Consider merely the characters of the flora in the 

 different zones of the earth. Quite different forms of plants 

 have been developed in the tropics than with us — yet 

 obviously in part essentiall}' through the direct influence of 

 the climate. Warmth and moisture have always, as at present, 

 stimulated tlie growth {i.e. the multiplication) of cells beyond 

 the limit which it reaches in colder climates, and this growth 

 necessarily produces new and more luxuriant developments. 



The following example shows to what a degree increased 

 growth results directly in change of form : the luxuriant 

 slioots wdiich spring from the stumps of trees, e/j. elms and 

 other forest trees, which have been cut dowai, often bear leaves 

 wliicli have a quite different shape from those the tree usually 

 bears, so that they have quite a strange appearance. This is 

 the immediate effect of unusually increased nutrition; the same 

 roots which previously supplied nourishment to the whole 

 tree have now only to provide for a few shoots. If such a 

 shoot grows into a tree, this again bears the ordinary leaves. 

 And if most of the roots of the stump were cut away so that 

 the shoot was reduced again to the usual supply of nutrition, 

 then likewise the new leaves would revert to the ordinary 

 form. Certain characters wliich are directly conditioned by 

 better nutrition, and others connected with them by correla- 

 tion, must obviously again disappear with the cessation of the 

 condition — thus certainly hunger causes leanness and feeble- 

 ness, over-feeding fat and laziness. In any case, experiments 

 continued for a year or two prove nothing. It is another 

 question whether specially abundant nutrition continued 



