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are mostly fertilized by night-flying itself often produced in immense promoths, and those which reserve their fusion. odours for the evening probably escape The beauty of alpine flowers is the visits of diurnal insects which almost proverbial. It consists either would consume their nectar without in the increased size of the individual effecting fertilization. The absence flowers as compared with the whole of odour in showy flowers and its pre- plant, in increased intensity of colour, ponderance among those that are or in the massing of small flowers into white, may be shown to be a fact dense cushions of bright colour; and it by an examination of the lists in is only in the higher Alps, above the Mr. Mongredien's work on hardy limit of forests and upwards towards trees and shrubs. He gives a list the perpetual snow-line that these of about one hundred and sixty characteristics are fully exhibited. species with showy flowers, and an- This effort at conspicuousness under other list of sixty species with fragrant adverse circumstances may be traced flowers; but only twenty of these to the comparative scarcity of winged latter are included among the showy insects in the higher regions, and to species, and these are almost all white the necessity for attracting them from flowered.
Of the sixty species with a distance. Amid the vast slopes of fragrant flowers, more than forty are debris and the huge masses of rock so white, and a number of others have prevalent in higher mountain regions, greenish, yellowish, or dusky and in- patches of intense colour can alone conspicuous flowers. The relation of make themselves visible and serve to white flowers to nocturnal insects is attract the wandering butterfly from also well shown by those which, like the valleys. Mr. Herman Müller's the evening primroses, only open their careful observations have shown, that large white blossoms after sunset. The in the higher Alps bees and most red Martagon lily has been observed other groups of winged insects are by Mr. Herman Müller to be fertilized almost wanting, while butterflies are by the humming - bird hawk moth, tolerably abundant; and he has diswhich flies in the morning and after- covered, that in a number of cases noon when the colours of this flower, where a lowland flower is adapted to exposed to the nearly horizontal rays be fertilized by bees, its alpine ally of the sun, glow with brilliancy, and has had its structure so modified as to when it also becomes very sweet- be adapted for fertilization only by scented.
butterflies. But bees are always (in To the same need of conspicuousness the temperate zone) far more abundthe combination of so many indivi- ant than butterflies, and this will be dually small flowers into heads and another reason why flowers specially bunches is probably due, producing such adapted to be fertilized by the latter broad masses as those of the elder, the should be rendered unusually congueldre-rose, and most of the Umbelli- spicuous. We find, accordingly, the feræ, or such elegant bunches as those yellow primrose of the plains replaced of the lilac, laburnum, horse-chestnut, by pink and magenta-coloured alpine and wistaria. In other cases minute species; the straggling wild pinks of flowers are gathered into dense heads, the lowlands by the masses of large as with Globularia, Jasione, clover, and flowers in such mountain species as all the Compositæ; and among the Dianthus alpinus and D. glacialis ; the latter the outer flowers are often de- saxifrages of the high Alps with veloped into a ray, as in the sunflowers, bunches of flowers a foot long, as in the daisies, and the asters, forming a Saxifraga longifolia and S. cotyledon, or starlike compound flower, which is forming spreading masses of flowers, 1 Trees and Shrubs for English Plantations,
as in S. oppositifolia ; while the soapby Augustus Mongredien. Murray, 1870.
2 Nature, vol. xi. pp. 32, 110.
worts, silenes, and louseworts are tation. The seeds of a particular species equally superior to the allied species may be carried to another country, may of the plains.
find there a suitable soil and climate, Again, Dr. Müller has discovered may grow and produce flowers, but if that when there are showy and in- the insect which alone can fertilize it conspicuous species in the same genus should not inhabit that country, the of plants, there is often a correspond - plant cannot maintain itself, however ing difference of structure, those with frequently it may be introduced or large and showy flowers being quite however vigorously it may grow. Thus incapable of self-fertilization, and thus may probably be explained the poverty depending for their very existence on in flowering-plants and the great prethe visits of insects; while the others ponderance of ferns that distinguishes are able to fertilize themselves should many oceanic islands, as well as the insects fail to visit them. We have deficiency of gaily-coloured flowers in examples of this difference in Malva others. This branch of the subject sylvestris, Epilobium angustifolium, Poly- is discussed at some length in my gonum bistorta, and Geranium pratense Address to the Biological Section of which have all large or showy flowers the British Association, but I may and must be fertilized by insects, -as here just allude to two of the most compared with Malva rotundifolia, striking cases. New Zealand is, in Epilobium parviflorum, Polygonum avi- proportion to its total number of culare, and Geranium pusillum, which flowering plants, exceedingly poor in have small or inconspicuous flowers,
handsome flowers, and it is correspondand are so constructed that if insects ingly poor in insects, especially in bees should not visit them they are able to and butterflies, the two groups which fertilize themselves.
so greatly aid in fertilization. In both As supplementing these curious these aspects it contrasts strongly with facts showing the relation of colour Southern Australia and Tasmania in in flowers to the need of the visits of the same latitudes, where there is a insects to fertilize them, we have the profusion of gaily-coloured flowers and remarkable, and on any other theory an exceedingly rich insect-fauna. The utterly inexplicable circumstance, that other case is presented by the Galain all the numerous cases in which pagos islands, which, though situated plants are fertilized by the agency of the on the equator off the west coast of wind they never have specially coloured South America, and with a tolerably floral envelopes. Such are our pines, luxuriant vegetation in the damp oaks, poplars, willows, beeches, and mountain zone, yet produce hardly a hazel ; our nettles, grasses, sedges, and single conspicuously-coloured flower; many others. In some of these the and this is correlated with, and no male flowers are, it is true, conspicuous, doubt dependent on, an extreme poas in the catkins of the willows and the verty of insect life, not one bee and hazel, but this arises incidentally from only a single butterfly having been the masses of pollen necessary to secure
found there. fertilization, as shown by the entire Again, there is reason to believe absence of a corolla or of those coloured that some portion of the large size and bracts which so often add to the beauty corresponding showiness of tropical and conspicuousness of true flowers. flowers is due to their being fertilized
The adaptation of flowers to be fer- by very large insects and even by tilized by insects—often to such an birds. Tropical sphinx-moths often extent that the very existence of the have their probosces nine or ten species depends upon it-has had wide- inches long, and we find flowers whose spread influence on the distribution of tubes or spurs reach about the same plants and the general aspects of vege length ; while the giant bees, and the 1 Nature, vol. ix. p. 104.
? See Nature, September 6th, 1876.
numerous flower-sucking birds, aid in been shown to be dependent on the same the fertilization of flowers whose class of general laws as those which corollas or stamens are proportion. have determined the form, the strucately large.
ture, and the habits of every living
thing. The complex laws and unI have now concluded this sketch expected relations which we have seen of the general phenomena of colour in to be involved in the production of the the organic world. I have shown rea- special colours of flower, bird, and sons for believing that its presence, insect, must give them an additional in some of its infinitely-varied hues, interest for every thoughtful mind; is more probable than its absence, and while the knowledge that, in all probthat variation of colour is an almost ability, each style of coloration, and Recessary concomitant of variation of sometimes the smallest details, have structure, of development, and of a meaning and a use, must add a new growth. It has also been shown how charm to the study of nature. colour has been appropriated and modified both in the animal and vege- Throughout the preceding discussion table world, for the advantage of the we have accepted the subjective phespecies in a great variety of ways, and nomena of colour--that is, our perthat there is no need to call in the aid ception of varied hues, and the mental of any
other laws than those of organic emotions excited by them—as ultimate development and “natural selection" facts needing no explanation. Yet they to explain its countless modifications. present certain features well worthy From the point of view here taken it of attention, a brief consideration of seems at once improbable and unneces- which will form a fitting sequel to the sary that the lower animals should present essay. have the same delicate appreciation The perception of colour seems, to of the infinite variety and beauty-of the present writer, the most wonderful the delicate contrasts and subtle har- and the most mysterious of our senmonies of colour—which are possessed sations. Its extreme diversities and by the more intellectual races of man- exquisite beauties seem out of prokind, since even the lower human races portion to the causes that are supposed do not possess it.
All that seems to have produced them, or the physical required in the case of animals, is a needs to which they minister. If perception of distinctness or contrast of we look at pure tints of red, green, colours; and the dislike of so many blue, and yellow, they appear so abcreatures to scarlet may perhaps be solutely contrasted and unlike each due to the rarity of that colour in other, that it is almost impossible to nature, and to the glaring contrast believe (what we nevertheless know to it offers to the sober greens
and be the fact) that the rays of light probrowns which form the general cloth- ducing these very distinct sensations ing of the earth's surface.
differ only in wave-length and rate The general view of the subject now of vibration; and that there is from given must convince us that, so far one to the other a continuous series from colour being—as it has some- and gradation of such vibrating waves. times been thought to be- unim- The positive diversity we see in them portant, it is intimately connected must then depend upon special adapwith the very existence of a large tations in ourselves ; and the question proportion of the species of the animal arises — for what purpose have our and vegetable worlds. The gay colours visual organs and mental perceptions of the butterfly and of the alpine flower becoine so highly specialised in this which it unconsciously fertilises while respect? When the sense of sight seeking for its secreted honey, are each was first developed in the animal beneficial to its possessor, and have kingdom, we can hardly doubt that
what was perceived was light only, own, do probably receive somewhat and its more or less complete with- similar impressions of colour ; but we drawal. As the sense became per- have no evidence to show that they fected, more delicate gradations of experience pleasurable emotions from light and shade would be perceived; colour itself when not associated with and there seems reason why a the satisfaction of their wants or the visual capacity might not have been gratification of their passions. developed as perfect as our own, or The primary nécessity which led to even more so, in respect of light and the development of the sense of colour, shade, but entirely insensible to differ- was probably the need of distinguishing ences of colour, except in so far as objects much alike in form and size, but these implied a difference in the differing in important properties ;quantity of light. The world would such as ripe and unripe, or eatable and in that case appear somewhat as we see poisonous fruits; flowers with honey it in good stereoscopic photographs; or without; the sexes of the same or and we all know how exquisitely of closely-allied species. In most cases beautiful such pictures are, and how the strongest contrast would be the completely they give us all requisite most useful, especially as the colours of information as to form, surface-texture, the objects to be distinguished would solidity, and distance, and even to some form but minute spots or points extent as to colour; for almost all when compared with the broad masses colours are distinguishable in a pho- of tint of sky, earth, or foliage against tograph by some differences of tint, which they would be set. Throughout and it is quite conceivable that visual the long epochs in which the sense of organs might exist which would dif- sight was being gradually developed ferentiate what we term colour by in the higher animals, their visual delicate gradations of some one cha- organs would be mainly subjected to racteristic neutral tint. Now such a two groups of rays--the green from capacity of vision would be simple as vegetation, and the blue from the sky. compared with that which we actually The immense preponderance of these possess; which, besides distinguishing over all other groups of rays would infinite gradations of the quantity of naturally lead the eye to become light, distinguishes also, by a totally specially adapted for their perception; distinct set of sensations, gradations and it is quite possible that at first of quality, as determined by differ- these were the only kinds of lightences of
wave lengths or rate of vibrations which could be perceived at vibration. At what grade in animal all. When the need for differentiation development this new and more com- of colour arose, rays of greater and plex sense first began to appear we of smaller wave-lengths would neceshave no means of determining. The sarily be made use of to excite the fact that the higher vertebrates, and new sensations required ; and we can even some insects, distinguish what thus understand why green and blue are to us diversities of colour, by no form the central portion of the visible means proves that their sensations of spectrum, and are the colours which colour bear any resemblance whatever are most agreeable to us in large to ours. An insect's capacity to dis- surfaces; while at its two extremities tinguish red from blue or yellow may we find yellow, red, and violet, colours be (and probably is) due to perceptions which we best appreciate in smaller of a totally distinct nature, and quite masses, and when contrasted with the unaccompanied by any of that sense of other two or with light neutral tints, enjoyment or even of radical distinct- We have here probably the foundaness which pure colours excite in us. tions of a natural theory of harmoniMammalia and birds, whose structure
ous colouring, derived from the order and emotions are so similar to our in which our colour-sensations have class of rays.
arisen, and the nature of the emotions animals on vegetation, and that man with which the several tints have been himself has been developed in the always associated. The agreeable and closest relation to it, we shall find, soothing influence of green light may probably, a sufficient explanation. The be in part due to the green rays having green mantle with which the earth is little heating power; but this can overspread caused this one colour to hardly be the chief cause, for the blue predominate over all others that meet and violet, though they contain less our sight, and to be almost always heat, are not generally felt to be so associated with the satisfaction of cool and sedative. But when we con
human wants. Where the grass is sider how dependent are all the higher greenest, and vegetation most abund1 There is reason to believe that our capa
ant and varied, there has man always city of distinguishing colours has increased found his most suitable dwelling place. even in historical times. The subject has In such spots hunger and thirst are attracted the attention of German philologists, and I have been furnished by a friend with
unknown, and the choicest productions some notes from & work of the late Lazarus of nature gratify the appetite and Geiger, entitled, Zur Entwickelungsgeschichte please the eye. In the greatest heats der Menschheit (Stuttgart, 1871). According of sunımer, coolness, shade, and mois-, to this writer it appears that the colour of grass and foliage is never alluded to as a
ture are found in the green forest beauty in the Vedas or the Zendavesta, though glades; and we can thus understand these productions are continually extolled for how our visual apparatus has become other properties. Blue described by terms especially adapted to receive pleasurdenoting sometimes green, sometimes black, showing that it was hardly recognised as a
able and soothing sensations from this distinct colour. The colour of the sky is never mentioned in the Bible, the Vedas, the The preceding considerations enable Homeric poems, or even in the Koran. The
us to comprehend, both why a percepfirst distinct allusion to it known to Geiger
tion of difference of colour has become is in an Arabic work of the ninth century: “Hyacinthine locks" are black locks, and developed in the higher animals, and Homer calls iron “violet-coloured.” Yellow also why colours require to be prewas often confounded with green, but, along sented or combined in varying proporwith red, it was one of the earliest colours to receive a distinct name. Aristotle names
tions in order to be agreeable to us. three colours in the rainbow-red, yellow,
But they hardly seem to afford a and green. Two centuries earlier Xenophanes sufficient explanation, either of thé had described the rainbow as purple, reddish, wonderful contrasts and total unlikeand yellow. The Pythagoreans admitted four
ness of the sensations produced in us primary colours - white, black, red, and yellow; the Chinese the same, with the addi.
by the chief primary colours, or of tion of green. If these statements fairly re- the exquisite charm and pleasure we present the early condition of colour-sensation derive from colour itself, as distinthey well accord with the view here main- guished from variously coloured objects, tained, that green and blue were first alone perceived, and that the other colours were
in the case of which association of ideas successively separated from them. These comes into play. It is hardly conceivlatter would be the first to receive names ; able that the material uses of colour hence we find purple, reddish, and yellow, to animals and to ourselves required first noticed in the rainbow as the tints to be separated from the widespread blue and
such very distinct and powerfullygreen of the visible world which required no contrasted sensations; and it is still distinctive colour-appellation. If the capacity less conceivable that a sense of deof distinguishing colours has increased in light in colour per se should have been historic times, we may perhaps look upon colour-blindness as a survival of a condition
necessary for our utilization of it. once almost universal; while the fact that it The emotions excited by colour and is still so prevalent is in harmony with the by music, alike, seem to rise above the view that our present high perception and level of a world developed on purely appreciation of colour is a comparatively
utilitarian principles. recent acquisition, and may be correlated with a general advance in mental activity.
ALFRED R. WALLACE.