Part 6

The conclusion that beauty is useful for the fertilization of the flower does not rest merely on the general phenomena of a summer meadow. It is confirmed by many other observations. Flowers are not merely attractive in themselves; they are frequently rendered attractive by their grouping. Sometimes flowers individually small are gathered into heads, or spikes, or bunches, or umbels, and so produce a more conspicuous effect than would result from a more equal distribution of the flowers; sometimes yet more minute flowers or florets are gathered together into what appears a single flower, and often have the outer florets so modified both in shape and colour as to produce the general effect of one very brilliant blossom, as in the daisy or the marigold.

Sometimes the same result is produced by "the massing of small flowers into dense cushions of bright colour."[4] This, as is well known, is of common occurrence with Alpine flowers; and this mode of growth, as well as the great size of many Alpine blossoms as compared with that of the whole plant, and the great brilliance of Alpine plants as compared with their congeners of the lowlands, have all been explained by reference to the comparative rarity of insects in the Alpine heights, and the consequent necessity, if the plants are to survive, that they should offer strong attractions to their needful friends.[5] A similar explanation has been offered for the brilliant colours of Arctic flowers.[6]

Furthermore, this curious fact exists, that of flowering plants a large number do not ripen or put forward their pistils and stamens at the same periods of their growth: in some cases the pistil is ready to receive the pollen whilst the anthers are immature and not ready to supply it: such are called proterogynous. In other cases the anthers are ripe before the pistil is ready to receive the pollen: these are proterandrous. In either case the same event happens--that the ovules can never be fertilized by the pollen of the same blossom, nor without some foreign agency, generally that of insects.

Lastly, there is a large number of plants, including a great proportion of those with unsymmetrical blossoms, of which the flowers have been shown to be specially adapted by various mechanical contrivances for insect agency. Nothing, as is well known, is more marvellous than the variety and subtlety of the arrangements for the purpose which exist in orchidaceous plants, as explained by the patience and genius of Mr. Darwin.

In view of these facts it would be impossible to deny that conspicuousness is one of the agencies in force for the fertilization of flowers; that, to use the recent language of Mr. Darwin, "flowers are not only delightful for their beauty and fragrance, but display most wonderful adaptations for various purposes."[7]

So far we have considered the evidence which is affirmative, and in favour of the explanation of the existence of beauty in flowers; we have found clearly that beauty, or rather conspicuousness, is in many cases useful to the plant. But beauty is by no means the only agency in this necessary process. On the contrary, the agencies actually in operation are very numerous.

As Mr. Darwin points out in the passage I have cited, and still more at large in his work "On the Different Forms of Flowers," a large proportion of existing plants are fertilized by the action of the wind; and again, many plants bear two kinds of flowers, the one conspicuous and attractive to insects, the other inconspicuous and which never open to admit the activity either of insects or of the wind. Moreover, there are various other agencies called into play. Some plants, such as the _Hypericum perforatum_, one of the commonest of the St. John's Worts, and probably the bindweed, are, it seems, fertilized by the withering of the corolla, which naturally brings the stamens into contact with the style, and so transfers the pollen grains from the one to the other.[8] Other plants, again, such as the common centaury (_Erythræa centaurium_) and the _Chlora perfoliata_, are fertilized by the closing of the corolla over the anthers and stigma, not in the death but in the sleep of the plant.[9] In the brilliant autumnal _Colchicum_, and in the _Sternbergia_, again, according to Dr. Kerner, Nature has recourse to a more complex machinery: the corolla first closes over the anthers, which are at a lower level than the stigma, and takes off some of the pollen; a growth of the corolla carries the pollen dust to the level of the stigma, and a second closing of the corolla transfers the pollen to the stigmatic surface. The pollen has been made to ascend to its proper place by an arrangement which reminds one of the man-engine of a Cornish mine.[10] A similar arrangement is described as occurring in the bright-flowered _Pedicularis_.[11]

Let us take another group of beautiful flowers which adorn our greenhouses and our tables: I mean the _Asclepiadæ_, to which the _Stephanotis_ and the _Hoya_ belong. The former is distinguished by the beauty of its scent as well as of its flowers. Both present flowers not merely conspicuous in themselves from their size, form, and colour, but conspicuous also by reason of their grouping. Here, if anywhere, we should expect that beauty should justify itself by its utility. But the facts appear to be just the other way. The pollen is collected together into waxy masses, which are arranged in a very peculiar manner on the pistil; and the pollen tubes pass from the pollen grains whilst still enclosed within the anthers, and so bring about fertilization without the intervention of insect agency. It is difficult to suppose the _Asclepiadæ_ can have become beautiful for the sake of an agency of which they never avail themselves.

Our common Fumitory has not very conspicuous flowers, but still they have considerable attractiveness of form and still more of colour, due both to the individual blossom and to their grouping together; and yet _Fumaria_ is said to be self-fertile.[12]

A much more brilliantly coloured member of the same family is the _Dicentra (Diclytra) spectabilis_, so familiar in our gardens. Any one who examines the flowers of this species will continually find the pollen grains transferred to the stigma without the slightest trace of the flower ever having opened so as to allow of insect agency. Dr. Lindley[13] has given an account of the mechanism for self-fertilization; and this flower has recently been the subject of an elaborate study by the German botanist, Hildebrand,[14] and he concurs in the view that the anthers inevitably communicate their pollen to the pistil, and that as the result of a very complicated and subtle arrangement of the parts, which it would be useless to attempt to describe without diagrams. But he believes that in addition to the arrangements for self-fertilization, another arrangement exists for producing cross-fertilization by insects; but as the plant has never produced seed under his observation, he is unable to tell whether one mode of fertilization is more useful than the other. I think the evidence of the self-fertilization is far clearer than that of the cross-fertilization.

Now, if the _Dicentra_ has become beautiful in order to attract insects, it must have done so through a long series of developments, for its adaptation to their agency is of the most complex kind. It is difficult to suppose either that, side by side with this development for cross-fertilization, there has been also developed another complex arrangement for self-fertilization, or that an earlier complex arrangement for self-fertilization should have survived through the changes necessary to render the flower fit for insect fertilization. The co-existence in one organism of two complex schemes for different objects, and the interlacing of those two schemes in one beautiful flower (which, if Hildebrand be right, occurs in the _Dicentra_), seem to be things very improbable if the beautiful flower has become what it is in the pursuit of one only of those objects. These speculations may be premature as regards the particular flower; but the co-existence of two modes of fertilization is not peculiar to _Dicentra_ and seems to furnish material for important reflection.

Yet one more plant must be considered. The _Loasa aurantiaca_ is a creeper which grows freely in our gardens, and has large and brilliantly coloured scarlet flowers turned up with yellow. Its seeds set freely in cultivation. The means by which fertilization is effected are--unless my observations have misled me--very peculiar. When the flower first unfolds, the numerous stamens are found collected together in bundles in depressions or folds of the petals; after a while the anthers begin to move, and one after the other the stamens pass upwards from their nests in the petals, and gather in a thick group round the style; subsequently a downward and backward movement begins, which brings the anthers against the pistils, and restores the stamens nearly to their old position, but with exhausted and faded anthers. I have never seen any insects at work on the flowers, and yet I find the plant to be a free seeder.

So long ago as 1840 M. Fromond enumerated several conspicuous flowers in which, according to his observations, fertilization was effected without the agency of either the wind or insects.[15] And much more recently an American writer, Mr. Meehan, has given a list of eleven genera, amongst others, in which he has observed the pistils covered with the pollen of the plant before the flower has opened, and in the one case which he submitted to the microscope, it was found that the pollen tubes were descending through the pistil towards the ovarium.[16] Amongst the genera he names were _Westaria_, _Lathyras_, _Ballota_, _Circes Genista_, _Pisum_, and _Linaria_.

The instances which I have given are mostly from plants familiar in our fields, our gardens, or our greenhouses. They are, I think, sufficient to make us pause before we conclude that all conspicuous flowers are fertilized by insect agency. It may be that Bacon's warning to attend as carefully to negative as to affirmative instances has been a little forgotten. Moreover, these instances seem to show that it would be a great error to suppose that all flowers are fertilized either by insects or by the wind; and it is probable that the more the subject is considered the more complex will the arrangements for fertilization be found to be.

The agencies to which I have last referred exist, it will be observed, in beautiful and conspicuous flowers; and yet act independently of that beauty and that conspicuousness: so that in each instance these facts are, on the utilitarian theory, unexplained and residual phenomena. They, therefore, demand earnest inquiry. For the existence of a single residual phenomenon is notice to the inquirer that he has not got to the bottom of his subject; that his theory is either not the truth or not the whole truth.

Do the facts justify us in concluding that insect fertilization is more beneficial to the plant than fertilization by the wind or any other agency? Do they afford any sufficient cause for that change from the one mode of fertilization to the other which has been suggested? The facts bearing on these questions are very remarkable; for, as we have already seen, many plants produce two kinds of blossom, the one conspicuous and the other inconspicuous; the one visited by insects, the other self-fertilizing. Recent observation shows that these cleistogamous flowers, as they are called, are present in a great variety of plants.[17] In the violet they are found to exist, being seen in the summer and autumn, when all the more brilliant flowers have gone. The one flower has everything in its favour--honey and a beauty of colour and of smell that has passed into a proverb--and it opens its blue wings to the visits of the insect tribe in the season of their utmost jollity and life. The other has everything against it: it is inconspicuous, scentless, ugly, and closed. And yet, which succeeds the better? which produces the more seed? The cleistogamous, and not the brilliant flowers: the victory is with ugliness, and not with beauty.

The same is true of the _Impatiens fulva_. This is an American plant, closely akin to the balsam of our gardens, which has now thoroughly established itself on the banks of some of our rivers, as the Wey, and the tributary stream that runs through Abinger and Shere. It has attractive flowers hung on the daintiest flower-stalks. It has also little green flowers that never open and almost escape attention; and yet they, and not the large flowers, are the great source of seed vessels to the plant--the great security that the life of the race will be continued.[18] Again, ugliness has borne away the palm of utility from beauty.

So, too, in America the same happens with the _Specularia perfoliata_: in shady situations all its flowers are said to be cleistogamous, and to be wonderfully productive and strong.[19]

The conditions of the problem in these cases are such as to make them of the last importance in our inquiry into the utility of beauty; for in each case we are comparing a conspicuous and an inconspicuous flower in the very same plant. The conditions seem to exclude the possibility of error in the result.

Two explanations have been suggested of the origin of these cleistogamous flowers: according to the one, they are the earliest form of the flowers; according to the other view, they are degraded forms of the more beautiful flowers.[20] For our purpose, it is immaterial whether of the two explanations is correct; for either the development of beauty has diminished the utility of the flower, or the loss of beauty has increased the utility: in either event, utility and beauty are dissociated the one from the other.

Another experiment Nature presents us with, in which the conditions are nearly, if not quite, as rigorously exclusive of error. The vast majority of orchidaceous plants are, as already mentioned, dependent on insect agency, for fertilization, and present a marvellous variety of contrivances for effecting cross-fertilization through their activity. But one of our orchids (the Bee orchis) is self-fertilized. I hardly know anything in vegetable life more striking or beautiful than to see its delicate pollinaria at a certain stage of its inflorescence descending on to the stigmatic surface and so yielding their pollen grains to the fertilization of their own blossom; and yet the Bee orchis has been found by observers to be as free a seeder as any of its tribe. Here the beauty and conspicuousness of the blossom, which are very great, are, as far as can be seen, useless; the plant gains nothing by the attractiveness which it offers, and the colouring and ornamentation of the blossom are, on the theory of utility, residual phenomena.

It is difficult to imagine that the change from wind or self-fertilization can, so to speak, commend itself to the flower on the score either of economy or success. If the anemophilous blossom must produce somewhat more pollen than the entomophilous, it saves the great expenditure of material and vital force requisite for the production of the large and conspicuous corolla. The one is fertilized by every wind that blows; the other, especially in the case of highly-specialized flowers like the orchids, may be incapable of fertilization except by a very few insects. The celebrated Madagascar orchid _Angræcum_ can be fertilized, it is said, only by a moth with a proboscis from ten to fourteen inches long--a moth so rare or local that it is as yet known to naturalists only by prophecy. It is difficult to suppose that it would be beneficial for the plant's chance of survival to exchange as the fertilizing agent the universal wind for this most localized insect.

And here another line of evidence comes in and demands consideration. The face of Nature, as we now see it, has not been always exhibited by the world. The flora, like the fauna, of the world has changed: how has it changed as regards the beauty of the flowers? Does it give any testimony to that _becoming_ beautiful of the flowers of plants to which Mr. Darwin refers? The answer is not a very certain one, by reason of the imperfection of the geological record, of the probability that beautiful plants, if they had existed, and had been of a delicate structure, would have perished and left no trace behind. But so far as an answer can be given, it is in favour of the increase of floral beauty in the vegetable world. The earliest flower known (the _Pothocites Grantonii_) occurs in the coal measures; its flowers cannot have been other than inconspicuous in themselves, though it is possible that by grouping they were made more attractive to the eye; in the period of the growth of the coal, when this plant lived, the vast forests seem principally to have been composed of trees without conspicuous blossoms, huge club mosses and marestails, and many conifers; in the earlier periods of this earth we have no trace of conspicuous blossom, and it is not till the upper chalk that the oaks and myrtles and _Proteaceæ_ appear as denizens of the forests. In like manner, if we refer to the appearance of insects on the earth, we have no clear trace in very early strata of those classes of insects which now do the principal work of fertilization for our conspicuous flowers. In the coal measures there have been found insects of the scorpion, beetle, cockroach, grasshopper, ant, and neuropterous families; but of a butterfly or moth there is only evidence of great doubt. It seems probable, then, and one cannot say more, that with the progress of the ages, flowers, as a whole, have become more conspicuous and attractive. But if we inquire whether the dull flowers of one era have grown into the conspicuous flowers of another, the answer is negative. The conifers of the coal age were anemophilous then, and are anemophilous still; they show no symptom of becoming more conspicuous; the same is true of the oaks of the chalk period, and of all other inconspicuous plants. The difference between conspicuous and inconspicuous flowers appears a permanent one; and the page of geology gives no evidence in favour of the supposed change.

Another observation must yet be made. Comparing flowers fertilized by insects and by the wind, it has never, so far as I can learn, been observed that the former are more certain of being set or more prolific than the latter; and, as already shown, the inconspicuous flowers are often more fertile than the conspicuous ones. What motive would there be, then, for the inconspicuous flowers of the early geologic periods to convert themselves into the brilliant corollas of our day?

Carefully considered, the passage which I have cited from Mr. Darwin does not account for the beauty of the flowers of plants at all; it accounts only for their conspicuousness, as the writer himself points out; and the two things are so different, that to account for the one is not even to tend to account for the other. If any one will consider the beauty of every inflorescence, whether conspicuous or not--a beauty which the microscope always makes apparent where the unaided eye fails to perceive it; or, again, the easily perceived beauty of many inconspicuous plants; or, lastly, the beauty of many conspicuous plants which does not tend to their conspicuousness--he will see how true this is.

For in many conspicuous flowers there are delicate pencillings and markings which certainly do not tend to make them such, but which nevertheless add greatly to their beauty, as we perceive it. In the regularly shaped flowers these markings often start from the centre of the blossom like radii, and they may be conceived as guiding the insects to the central store of honey. Such guidance can hardly be needful, as the shape of the flower itself generally does all, and more than all, that the markings can do in the way of guidance. But it is by no means true that all the markings lead to the centre of the flower: many are transverse; many are marginal; some are by way of spot.

Again, take the irregularly shaped flowers, which are supposed to be the exclusive subjects of insect fertilization; how infinite are the beauties of the flower over and above those which make it conspicuous, or can assist to guide the insect. Take the orchids, for example: the labellum is generally the landing-place of the insect visitors; but the other flower-leaves are almost always the subjects of a vast display of delicate beauty which cannot be accounted for by the necessity of conspicuousness or guidance. All this beauty is, on the theory in question, an unexplained fact.

But, again, take the grasses, which depend for fertilization exclusively on the wind, and have no need to woo the visits of the insects. The beauty of the markings of the inflorescence of many of the grasses is very great, though far from conspicuous: take the delicately banded flowers of our quaking grasses; take the rich crimson of the foxtails; take the brilliant yellow of the Canary _Phaleris_; and it is impossible to refuse the attribute of beauty in colour to the wind-loving grasses. And all this beauty is unexplained on the theory in question.

It is impossible to speak of the grasses and not to have the mind recalled to the beauty that resides in form as contrasted with colour. Elegance, grace of form, characterizes most (but not all) plants, whether fertilized by the wind or by insects; and yet this grace, in many cases, perhaps in most, adds nothing to their conspicuousness. It is, on the theory in question, a piece of idle beauty; and yet it is all-pervading--a persistent, though not universal, characteristic of the vegetable world.

But to revert to conspicuousness. It is not true to say that all self-fertilized plants have inconspicuous flowers. I have adduced the _Stephanotis_ and _Hoya_ on this point. Nor is it true to say that all anemophilous flowers are inconspicuous as compared with the green of their leaves. The large but delicate yellow groups of the male flowers of the Scotch pine (not to travel beyond very familiar plants) are very conspicuous in the early summer--much more so, to my eye at least, than many flowers which are supposed to stake their lives on attraction by being conspicuous. Hermann Müller has observed on this same fact, and considers it to be clear that the display of colour can be of no use to the plant, and must therefore be regarded as "a merely accidental phenomenon,"[21]--_i.e._, a phenomenon not accounted for by utility.

The crimson flowers of the larch, again, are certainly very conspicuous as well as beautiful on the yet leafless boughs; and yet they owe nothing to insects.

One other remark must be made on this passage from Mr. Darwin which has formed my text. It does not pretend to account for the production of beauty or even of conspicuousness. It only seeks to account for the accumulation of that quality in certain plants, and its comparative absence in others. The tendency in Nature to produce beauty is a postulate in Mr. Darwin's theory.

The beauty of mountain blossoms has been referred to as supporting the utility of beauty: it is not perfectly clear that even this can be accounted for merely by the need of attracting insects. It is said by the American writer to whom I have already referred, Mr. Meehan, that the flowers of the Rocky Mountains are beautifully coloured, produce as much seed as similar ones elsewhere, and yet that there is a remarkable scarcity of insect life--so great, I understand him to mean, as to render it highly improbable that the races of the flowers can be perpetuated by insect agency.