NA TURE 



501 



THURSDAY, APRIL 3, 1879 



COLOUR IN NATURE 



The Colour Sense: its Origin and Devtloptnent. An 

 Essay in Comparative Psychology. By Grant Allen, 

 B.A. (London : Triibner and Co., 1879.) 



THIS interesting and suggestive work deals with the 

 whole question of colour in nature, and more espe- 

 cially with its manifestations in the organic world and 

 the complex colour reactions between plants and animals. 

 It traces the origin of the colour sense in insects to their 

 visits to primeval flowers in order to feed upon the pollen, 

 and in birds to their seeking for fruits, whose seeds they 

 dispersed and whose colours were developed to attract 

 them. It thus attempts to show that the very existence 

 of most of the brilliant colours of the organic world is due 

 to the influence of the colour sense in animals. The 

 author adopts, with some reservations, Mr. Darwin's 

 theory of sexual selection to account for the colours of 

 most animals, and he endeavours to show that only those 

 groups display beautiful colours in which a taste for 

 colour has been aroused by the influence of flowers, fruits, 

 or brilliant insects, their habitual food. AU these subjects 

 are treated in a very thorough manner, with a wealth of 

 illustration, a clearness of style, and a cogency of reason- 

 ing, which make up a most attractive volume ; and though 

 we may not agree with all the author' s conclusions, and 

 may even doubt the accuracy of some of his facts, we 

 cannot but admit that he has placed the whole subject 

 before us in a way that must engage the attention both of 

 the man of science and the general reader. We will now 

 proceed to give an outline of the whole work, dwelling 

 here and there on the more interesting points, and 

 especially on those where we venture to differ from the 

 conclusions arrived at. 



After an introductory chapter, the contents of which 

 are above indicated, an excellent account is given of the 

 nature of light, and of those peculiarities of the aether- 

 waves which produce in us the sensations of light and 

 colour. The third chapter deals with the organ of vision, 

 giving an account of its earliest appearance and progres- 

 sive complexity in the animal kingdom, and of the struc- 

 ture of the eyes of the higher animals, and the relation of 

 their parts to the perception of light and of differences of 

 colour. One of the most important facts here brought 

 out is, that the complex mechanism required to produce 

 vision has been several times independently evolved — 

 the eye of the bee, of the cuttle-fish, and of the eagle have 

 each apparently been separately developed from unlike 

 'emote sightless ancestors. 



The next chapter is a long and very interesting one, on 

 ■'Insects and Flowers." It deals with the origin and 

 development of these two classes of organisms and their 

 actions and reactions on each other. It is full of interest- 

 ing facts ; and the discussion of the mode of origin of the 

 colours of flowers by a reference to the conditions under 

 which colour appears normally in living plants is espe- 

 cklly instructive ; the generalisation being arrived at that 

 tltt leaves which create or store up energy for the plant 

 are green, while whenever leaves lose this function and 

 become expenders of energy they lose the green tint and 

 Vol. XIX. — No. 492 



acquire various other colours ; growing shoots, young 

 leaves, buds, stamens and stigmas, and their protecting 

 scales, are almost always variously coloured. The rudi- 

 ments of colour being thus always ready in the floral 

 organs, it is not surprising that flowers have been sepa- 

 rately developed in monocotyledons and dicotyledons, 

 and also probably many times over in each of these 

 divisions. 



In this part of his work the author exhibits his tendency 

 to trust far too much to negative evidence, especially to 

 that afforded by geolog}'. He speaks of the carboniferous 

 epoch as presenting a green jungle of ferns and club-moss, 

 " in which there is no trace of bee or moth or joyous 

 butterfly;" while "scarlet berry and crimson blossom, 

 gorgeous bird, and painted insect were aU equally absent 

 from the unvaried panorama of green overhead and brown 

 beneath." As the flora preserved to us in the coal- 

 measures was almost certainly that of swamps only, we 

 cannot possibly tell what existed on the uplands and 

 mountains of that period. The enormous differentia- 

 tion of flowering plants, and the comparatively little 

 change they seem to have undergone during the whole 

 tertiary period would lead to the inference that they 

 may have already existed in some variety during the car- 

 boniferous epoch ; while the actual discovery of a butterfly 

 in the lower oolite, and of a well preserved wing of what 

 appears to be a large moth in the carboniferous shales of 

 Belgium,^ renders it quite possible that coloured flowers 

 and gay butterflies were then in existence. The state- 

 ments as to the time when the different orders of insects 

 first came into being (quoted at p. 68) are quite worthless 

 when we consider how rare must be the conditions lead- 

 ing to the preservation of winged insects, and they are 

 already contradicted by well-known palaeontological facts. 

 Another statement that seems equally open to doubt is, 

 that even in early tertiary times there were no orchids 

 (p. 97), a statement founded on the generalisation that 

 entomophilous monocotyledons are later productions than 

 entomophUous dicotyledons, because the perianth of the 

 former is usually less specialised. But surely in orchids 

 the perianth is more highly specialised than in any exist- 

 ing flowers whatever ; and if we take into account the 

 world-wide distribution of these plants, their immense 

 richness in genera and species, and their wonderful com- 

 plexity of structure, we must consider them as among the 

 most ancient instead of the most recent of flowers. They 

 are also exceptions to the general rule of the size of the 

 flower being in inverse proportion to its special adapta- 

 tion to insect fertilisation ; of which the large but simple 

 lilies and tulips as contrasted with the small but complex 

 labiates, are quoted as examples. 



The next chapter, on the colour sense in insects, sets 

 forth both the direct and the indirect evidence on this 

 question; such as Sir John Lubbock's experiments on 

 bees and wasps, the mimicking insects which deceive 

 other insects, the clear relation of coloured flowers to the 

 visits of insects, the fact of insects often visiting hundreds 

 of the same species of flower in succession, &c. This 

 chapter concludes with a striking picture of the vast 

 effect which has been produced on the appearance of 

 external nature by insect agency, " which has turned the 



' Breyeria hcrinensis, "Annales de la Sodettf Entcmologiqiie de Be!- 

 gique," t. xviii. PI. v. (Photograph). 



