330 LAWS OF VARIATION, Chap. XXV. 



cold better than those with lighter complexions from the 

 north ; but no doubt such statements are liable to error. 



In the second chapter on Selection I have given several 

 cases proving that with animals and plants differences in 

 colour are correlated with constitutional differences, as shown 

 by greater or less immunity from certain diseases, from the 

 attacks of parasitic plants and animals, from scorciiing by the 

 sun, and from the action of certain poisons. When all the 

 individuals of any one variety possess an immunity of this 

 nature, we do not know that it stands in any sort of correlation 

 with their colour; but when several similarly coloured 

 varieties of the same species are thus characterised, whilst 

 other coloured varieties are not thus favoured, we must believe 

 in the existence of a correlation of this kind. Thus, in the 

 United States purple-fruited plums of many kinds are far 

 more affected by a certain disease than green or yellow-fruited 

 varieties. On the other hand, yellow-fleshed peaches of 

 various kinds suffer from another disease much more than the 

 white-fleshed varieties. In the Mauritius red sugar-canes 

 are much less affected b}'' a particular disease than the white 

 canes. White onions and verbenas are the most liable to 

 mildew ; and in Spain the green- fruited grapes suffered from 

 the vine-disease more than other coloured varieties. Dark- 

 coloured pelargoniums and verbenas are more scorched by the 

 sun than varieties of other colours. Eed wheats are believed 

 to be hardier than white ; and red-flowered hyacinths were 

 more injured during one particular winter in Holland than 

 other coloured varieties. With animals, white terriers suffer 

 most from the distemper, white chickens from a parasitic 

 worm in their trache£e, white pigs from scorching by the sun, 

 and white cattle from flies ; but the caterpillars of the silk- 

 moth which yield white cocoons suffered in France less from 

 the deadly parasitic fungns than those j)roduciiig yellow silk. 



The cases of immunity from the action of certain vefj;etabie 

 poisons, in connexion with colour, are more interesting, and 

 are at present wholly inexplicable. I have already given a 

 remarkable instance, on the authority of Professor \Vyman, of 

 all the hogs, excepting those of a black colour, suffering 

 severely in Virginia from eating the root of the Lachnanthcs 



