656

DYEING AND CALICO PRINTING.

temperature of the torrid zone, we are met with the following phenomena :—■The leaves and flowers of plants kept in dark places are pale and bleached inappearance, irrespedtive of the temperature to which they are exposed, as, forinstance, the shoots of a potato kept in a dark cellar. The diurnal Lepidopteraof all countries are much more splendid than the nodturnal species of thesame distridls. The under surface of the wings of butterflies is often as gailycoloured as the upper. But it is as nearly as much exposed to light, bothwhen the insedt is flying and when it is in a state of repose. In moths, onthe other hand, when the under surface is very little exposed to light, itscolours are sombre and monotonous. Nodturnal beetles of the Lamellicornorder, such as the Geotrupidse, exhibit dull and dark shades, whilst theCetoniads, the diurnal members of the same order, might be charadterised asanimated jewels. Among birds and mammals the same general rule prevails ;those of sunny climates are brighter than those of cold and gloomy countries;diurnal species are more gaily clad than the nodturnal, and in one and thesame species the parts most exposed to light—the head, back, and shoulders—are more highly coloured than the belly, and, in birds, the sides wherecovered by the wings. The difference in appearance between the sunny andthe shady side of a peach or an apple is well known, as also the circumstancethat the stems of plants, green above the surface of the soil where fully ex-posed to light, are pale or colourless below, where the light is excluded. Onthe faith of these, and similar phenomena which do not require to beindividually enumerated, the colouration of organic bodies is generally con-sidered to be a diredt result of light, increasing in depth and brilliance withits intensity, and fading away in its absence.

But there are, on the other hand, indisputable fadts which must tend tomodify this conclusion. In the vegetable world we find roots completelyexcluded, of course, from the light during the whole life of the plant, and yetcoloured or even containing powerful colouring matters. As commonexamples we may cite the carrot, the Eschscholtzia, and madder, with itscongeners. It has been often pointed out that that the timber of treesgrowing in cold climates is pale, whilst in the torrid zone deep colours aregenerated, as in the dye-woods, ebony, and others. But the heart-wood of atree is certainly not exposed to any diredt adtion of the solar rays. In theanimal world it must be remarked that subterranean and nodlurnal speciescannot be indiscriminately pronounced to be pale, bleached, or etiolated. Onthe contrary, many of them, such as the Harpalid and Geotrupid beetles,certain spiders, &c., exhibit intense colours, such as deep browns or blacks.The common badger presents a striking exception to the rule that the upperor sunny side of animals is more deeply coloured than the belly. Two generaof moths, the Arctias and Catocalas , display colours as gorgeous as anybutterfly—scarlet, crimson, rose, and blue. Yet these colours are almost con-fined to the hinder wings, which are completely and closely covered by theanterior pair when the insedt is at rest, and are only unfolded on the night airwhen it is flying. Perhaps the most nodturnal quadrupeds are the Felida;, yetamongst them we find some of the most gaily coloured species of mammalians.Again, though plants allowed to grow in darkness are devoid of their naturalcolours, animals do not, under the same circumstances, undergo a correspondingchange. This has been proved by diredt experiment. Caterpillars of Vanessa lo