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sedges, and many others. In some of these the male flowers are, it is true, conspicuous, as in the catkins of the willows and the hazel, but this arises incidentally from the masses of pollen necessary to secure fertilization, as shown by the entire absence of a corolla or of those coloured bracts which so often add to the beauty and couspicucusness of true flowers.
The Same Theory of Colour Applicable to Animals and Plants.—It may be thought that this absence of colour where it is not wanted is opposed to the view maintained in the earlier part of the preceding chapter, that colour is normal and is constantly tending to appear in natural objects. It must be remembered, however, that the green colour of foliage, due to chlorophyll, prevails throughout the greater part of the vegetable kingdom, and has, almost certainly, persisted through - long geological periods. It has thus acquired a fixity of character which cannot be readily disturbed ; and, as a matter of fact, we find that colour rarely appears in plants except in association with a considerable modification of leaf-texture, such as occurs in the petals and coloured sepals of flowers. Wind-fertilized plants never have such specially organized floral envelopes and, in most cases, are entirely without a calyx or corolla. The connection between modification of leaf-structure and colour is further seen in the greater amount and variety of colour in irregular than in regular flowers. The latter, which are least modified, have generally uniform or but slightly varied colours; while the former which have undergone great modification, present an immense range of colour and marking, culminating in the spotted and variegated flowers of such groups as the Scrophularinca
and Orchidea. The same laws as to the conditions of a maximum production of colour are thus found to obtain both in plants and animals.
Relution of the Colours of Flowers and their Geographical Distribution.—The adaptation of flowers to be fertilized by insects-often to such an extent that the very existence of the species depends upon it-has had wide-spread influence on the distribution of plants and the general aspects of vegetation. The seeds of a particular species may be carried to another country, may find there a suitable soil and climate, may grow and produce flowers; but if the insect which alone can fertilize it should not inhabit that country, the plant cannot maintain itself, however frequently it may be introduced or however vigorously it may grow. Thus may probably be explained the poverty in floweringplants and the great preponderance of ferns that distinguishes many oceanic islands, as well as the deficiency of gaily-coloured flowers in others. This branch of the subject is discussed at some length in my Address to the Biological Section of the British Association, but I may here just allude to two of the most striking cases. New Zealand is, in proportion to its total number of floweringplants, exceedingly poor in handsome flowers, and it is correspondingly poor in insects, especially in bees and butterflies, the two groups which so greatly aid in fertilization. In both these aspects it contrasts strongly with Southern Australia and Tasmania in the same latitudes, where there is a profusion of gaily-coloured flowers and an exceeding rich insect-fauna. The other case is presented by the Galapagos islands, which, though
" See Chapter VII. of this rolume.
situated on the equator off the west coast of South America, and with a tolerably luxuriant vegetation in the damp mountain zone, yet produce hardly a single conspicuously-coloured flower; and this is correlated with, and no doubt dependent on, an extreme poverty of insect life, not one bee and only a single butterfly having been found there.
Again, there is reason to believe that some portion of the large size and corresponding showiness of tropical flowers is due to their being fertilized by very large insects and even by birds. Tropical sphinx-moths often have their probosces nine or ten inches long, and
ind flowers whose tubes or spurs reach about the same length ; while the giant bees, and the numerous flower-sucking birds, aid in the fertilization of flowers whose corollas or stamens are proportionately large.
Recent Vieu's as to Direct Action of Light on the Colours of Flowers and Fruits. — The theory that the brilliant colours of flowers and fruits is due to the direct action of light, has been supported by a recent writer by examples taken from the arctic instead of from the tropical flora. In the arctic regions vegetation is excessively rapid during the short summer, and this is held to be due to the continuous action of light throughout the long summer days. “The further we advance towards the north the more the leaves of plants increase in size as if to absorb a greater proportion of the solar rays. M. Grischach says, that during a journey in Norway he observed that the majority of deciduous trees had already, at the 60th degree of latitude, larger leaves than in Germany, while M. Ch. Martins has made a similar observation as regards the leguminous plants
cultivated in Lapland.”] The same writer goes on to say that all the seeds of cultivated plants acquire a deeper colour the further north they are grown, white haricots becoming brown or black, and white wheat becoming brown, while the green colour of all vegetation becomes more intense. The flowers also are similarly changed: those which are white or yellow in central Europe becoming red or orange in Norway. This is what occurs in the Alpine flora, and the cause is said to be the same in both—the greater intensity of the sunlight. In the one the light is more persistent, in the other more intense because it traverses a less thickness of atmosphere.
Admitting the facts as above stated to be in themselves correct, they do not by any means establish the theory founded on them; and it is curious that Grisebach, who has been quoted by this writer for the fact of the increased size of the foliage, gives a totally different explanation of the more vivid colours of Arctic flowers. He says—“We see flowers become larger and more richly coloured in proportion as, by the increasing length of winter, insects become rarer, and their co-operation in the act of fecundation is exposed to more uncertain chances." (Vegetation du Globe, vol. i. p. 61– French translation.) This is the theory here adopted to explain the colours of Alpine plants, and we believe there are many facts that will show it to be the preferable one. The statement that the white and yellow flowers of temperate Europe become red or golden in the Arctic regions must we think be incorrect. By roughly
i Revue des Deux Monues, 1877. “ La Vegetation dans les hautes Latitudes,” par M. Tisserand.
tabulating the colours of the plants given by Sir Josephz Hooker' as permanently Arctic, we find among fifty species with niore or less conspicuous flowers, twenty-five white, twelve yellow, cight purple or blue, three lilac, and two red or pink; showing a very similar proportion of white and yellow flowers to what obtains further south.
We have, however, a remarkable flora in the Southern Hemisphere which affords a crucial test of the theory of greater intensity of light being the direct cause of brilliantly coloured flowers. The Auckland and Campbell's Islands south of New Zealand, are in the same latitude as the middle and the south of England, and the summer days are therefore no longer than with us. The climate though cold is very uniform, and the Weather "very rainy and stormy.” It is evident, then, that there can be no excess of sunshine above what we possess; yet in a very limited flora there are a number of flowers which-Sir Joseph Hooker statesare equal in brillianey to the Arctic flora. These consist of brilliant gentians, handsome veronicas, large and magnificent Compositæ with purple flowers, bright ranunculi, showy Umbelliferæ, and the golden flowered Chrysobactron Rossii, one of the finest of the Asphodelea.? All these fine plants, it must be remembered, are peculiar to these islands, and have therefore been developed under the climatal conditions that prevail there; and as we have no reason to suppose that these conditions have undergone any recent change we may be
1"On the Distribution of Arctic Plants,” Linn. Trans. vol. xxiii. (1862.) * Coloured figures of all these plants are given in the Flora Antarctica, vol. i.