from the action of certain poisons. When all the
individuals of any one variety possess an immunity of this nature, we
cannot feel sure that it stands in any sort of correlation with their
colour; but when several varieties of the same species, which are similarly
coloured, 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 by 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.
Red wheats are believed to be hardier than white; whilst 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 tracheae, 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 fungus than those producing yellow silk.

The cases of immunity from the action of certain vegetable 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 Wyman, of all the hogs, excepting those of a black colour,
suffering severely in Virginia from eating the root of the _Lachnanthes
tinctoria_. {337} According to Spinola and others,[840] buckwheat
(_Polygonum fagopyrum_), when in flower, is highly injurious to white or
white-spotted pigs, if they are exposed to the heat of the sun, but is
quite innocuous to black pigs. By two accounts, the _Hypericum crispum_ in
Sicily is poisonous to white sheep alone; their heads swell, their wool
falls off, and they often die; but this plant, according to Lecce, is
poisonous only when it grows in swamps; nor is this improbable, as we know
how readily the poisonous princip