ae5be TCE eens ako Soe BS Sees pose ee Grits potas, ee Sar Pen plincecukie tees G oa LAA ee ne AAA rite poche nag opie E ; : De pete nad meee at Ree eet tac teet states ? heretics ate pth Seen See em tae Soe Suntan ieey Rpts aces ph ag eaeta tae Cee sos aha See nak toe Sopa ag a) Sst Pattee ay pate ten ee as Sey pees Pease Rd eats =~ ‘ee _ ALBERT R. MANN LIBRARY NEw: YorK STATE COLLEGES OF ae ‘AGRICULTURE AND HoME EcoNoMIcs AT CoRNELL UNIVERSITY . so University Libra QK 653.K39 wi AAA FLOWERS AND THEIR UNBIDDEN GUESTS. FLOWERS AND THEIR UNBIDDEN GUESTS By Dr. A. KERNER PROFESSOR OF BOTANY IN THE UNIVERSITY OF INNSBRUCK WITH A PREFATORY LETTER BY CHARLES DARWIN, M.A., F.R.S. The Translation Rebised and Edited By W. OGLE, M.A., M.D. SOMETIME FELLOW OF CORPUS CHRISTI COLLEGE, OXFORD WITH ILLUSTRATIONS. (ARBOR _SCIENTIA LONDON C. KEGAN PAUL & CO.,1 PATERNOSTER SQUARE 1878 The rights of Translation and of Reproduction are reserved. PREFATORY LETTER. My pear Dr. OciE,—I am extremely glad to hear that you have undertaken to edit Kerner’s work on Flowers and their Unbidden Guests; for it opens out a highly original and curious field of research. It is possible that some of Kerner’s generalisations may hereafter require to be slightly modified; but I feel sure that every remark which he has made well deserves careful consideration. The beauty and poetry of flowers. will not be at all lessened -to the general observer, by his being led through Kerner’s investiga tion to notice various small, and apparently quite unimportant, details of structure,—such as the presence of differently directed hairs, viscid glands, etc., which prevent the access of certain insects, and not of others. He will, I believe, come to the conclusion that flowers are not only delightful from their beauty and fragrance, vi Prefatory Letter. but display most wonderful adaptations for various purposes. I cordially wish that your translation may find many readers, not so much for your sake as for theirs. Believe me very faithfully yours, CHARLES DARWIN. Down, Beckenuam, Kent, August 17, 1878. EDITOR’S PREFACE. THE year 1862 will ever be a memorable date in the annals of botany, as that in which Mr. Darwin pub- lished his classical work on the fertilisation of Orchids, and in so doing disclosed a wide and unexplored region to the research of physiological botanists. Since then a huge mass of observations has been gradually ac- cumulating, the general result of which is to con- firm with great certainty the truth of the Darwinian generalisation, that, so far at any rate as plants are concerned, “ Nature abhors perpetual self-fertilisation.” It has been shown that in the vast majority of flower- ing plants—exceptions may here be disregarded— appliances exist which will at any rate secure a more or less frequent intercross, and that in many of them, moreover, these appliances completely exclude the possibility of self-fecundation. The agency by which this result is obtained, and the pollen transported from one flower to another, may be either inanimate or animate. In the former case it is the wind, or exceptionally (Valisneria spiralis) water. Plants thus fertilised pre- sent certain peculiarities. Their pollen, for instance, is dusty, so as to be easily diffused by a slight current. viii Preface. Their flowers have inconspicuous petals, or none; ex- hale no sweet odour; secrete no sweet nectar. They have no object in attracting insects, and consequently appeal to none of their senses. It is quite otherwise when the agency of pol- lination is animate. The animate agent is in some comparatively few instances a bird, but as a gene- ral rule is an insect. These must be allured to the flower; and this accordingly appeals to their sight or smell by brilliant colours and by attraetive scents. These colours and these scents draw the insect to the flower from a distance; but by themselves they would be but empty gratifications, unprofitable to insect and to flower alike. Something more sub- stantial must be offered; something that will prevent the insect from merely loitering about the flower in idle satisfaction, and that will induce it to probe the recesses of the blossoms, and in so doing to transfer the pollen of one flower to the stigma of another. This further allurement is addressed to the palate ; and though in some cases it is nothing more than the pollen itself, in most it is supplied by the secretion of a sweet fluid, the so-called nectar. Now Nature, who at first sight often appears a prodigal, is always found on closer examination to be the most rigid of economists. If no insects are to be allured, she gives, as we have seen, no nectar; she cuts off the bright petals, and suppresses the attractive Preface. ix odours. Nor even when a bait is wanted will she give it one minute sooner than necessary. The bril- liancy, the scent, and the nectar are only furnished when the flower is ready for its guests, and requires their presence; just as a thrifty housewife lights her candles when the first guest is at the door. The immature bud is furnished with no such attractions. Still more, even when the flower is mature, when its pollen is ready for transference or its stigma for fecundation, when all the allurements are consequently displayed and insects invited to the feast, she still shows her economy. Guests might come who were not of sufficient importance, and the banquet be wasted on them; for it is only when insects have a certain shape, size, or weight that she requires their visits, and can use them profitably for her purposes. She requires, moreover, that they shall make their entrance by the main portal, which she has specially adapted to suit their and her requirements. All insig- nificant and unremunerative visitors, all such, more- over, as would creep in by a back entrance, must be kept out; and the purpose of this treatise is to show by what various contrivances this exclusion is effected. The subject is new, though a branch of the tree planted by Mr. Darwin. For if some feeble ink- lings of the existence in flowers of such excluding contrivances may have occurred to other persons,— nay, may even have been distinctly enunciated by B x Preface. them,—the fruitful recognition of the fact and its establishment by convincing evidence is to be found for the first time in this treatise of Kerner. To him exclusively will be due the merit of having interpreted the meaning of a vast number of floral structures, which before he wrote were passed over as purposeless. It is curious, however, to note that so long ago as in the last century, Erasmus Darwin, in his Loves of the Plants, should have remarked on the protective function of one of the appliances described by Kerner, namely, of the water-cups formed by the connate leaves of the teasel; and should even have alluded to the nectar as one of the treasures to be thus guarded.’ As this writer was of course quite ignorant of the true relations between insects and flowers, which have been made known to us by his grandson, it is not easy to see why he should have supposed that the nectar required protection, or indeed what use at all he can have ascribed to this secretion. It is in a later and quite recent author that we find the first clear anticipation of Kerner, Mr. Belt, in his charming work on Nica- ragua (p. 131-3), distinctly recognises the fundamental point in this essay of Kerner. “Many flowers,” he says, “have contrivances for preventing useless insects from obtaining access to the nectaries;” and after illustrating this statement by a detailed account of the 1See Mr. Francis Darwin: Quart. Journ. of Micros. Science, xvii, 269. Preface. xl contrivances for this purpose in Digitalis purpurea, he adds, “ Great attention has of late years been paid by naturalists to the wonderful contrivances amongst flowers to secure cross-fertilisation. But the structure of many cannot, I believe, be understood unless we take into consideration not only the beautiful adapta- tions for securing the services of the proper insect or bird, but also the contrivances for preventing insects that would not be useful from obtaining access to the nectar ;” and he instances the lengthy spur of Angrecum sesquipedale. These are the only anticipations of Kerner that I have found in books, though doubtless there may be, nay probably are, others unknown to me. I may, however, perhaps be forgiven the little egotism that prompts me to give the following account of observations made by myself. In the early spring of 1876 I was spending a holiday at the Italian lakes. Close to my inn was a bank profusely covered with rough grass and flowers, amongst which Lychnis viscaria was pre-eminent. Having it constantly before me, I was led to speculate as to the possible uses of the viscous secretion, which in this plant forms a ring round the stem, just‘above each of the higher nodes. I was not then acquainted with the passage cited above from Mr. Belt’s book, and my first surmise was that the viscous matter might act as a trap for small insects, which were to be seen xii Preface. adhering to it in numbers, and that these insects might then be digested and absorbed. But this I soon saw could not be the case. The viscous matter was without taste or smell, and clearly had no attractiveness to insects, for none were ever to be seen buzzing about it. Moreover, a few days’ observation showed that the adhering insects were in fact not digested, nor even dissolved. Might not its use then be to keep insects that mere too small to effect cross-fertilisation, and especially to keep ants, from crawling up the stem to the flowers ? That it did as a matter of fact keep them off was plain. The bank swarmed with ants, which were to be seen running up and down many of the other flowers in numbers. But not a single ant did I ever find climbing up a lychnis-stem. If one was put on a sticky ring it adhered there, and never succeeded in getting free. The ants seemed to have found out by previous experience how useless it was to try to mount this plant, and rarely was one to be seen even on the part of the stem which was below the undermost viscid ring. That the stem should only be viscid in part and not throughout was intelligible enough, on the principle of economy. But why were not the viscid rings reduced on the same principle to a single one? Seeing how efficacious and utterly impassable the viscid matter was, it seemed as though a single ring would do as well as a series. The following appeared to me to be a possible ex- Preface. Xlil planation. Were there but one ring, the blades of grass and other plants that grew intermixed with the lychnis, and which came into contact with it at all kinds of points and all kinds of angles, would serve as so many ladders by which the ant might reach a point on the stem above the solitary ring, and so get at the nectar. The repeti- tion of the rings would make this impossible, unless, indeed, the ladder chanced to be set against the flower itself, or against the uppermost extremity of the stem. Doubtless, if the viscid ring were at the very top of the stem, or if the calyx itself were viscid, the same result would be obtained. And as a matter of fact this was the arrangement in sundry plants, as in the Nottingham Catch-fly (Silene nutans), where only the calyx and up- permost stem were viscid, whereas in the English Catch- fly (S. Anglica) the whole plant was sticky. The condi- tion of the Lychnis viscaria seemed intermediate to these. The stem might perhaps have once been sticky all over ; and then the viscidity have become limited on econo- mical grounds to the nodes, and might in further ages perhaps become limited still further to the top of the stem. Nor were indications of such a possible event wanting, for already the lowest nodes of the stem were, as I found, destitute of viscid secretion. On my return home, I propounded my hypothesis as to the functional significance of viscidity to Mr. Darwin, of whose inexhaustible kindness in listening patiently to the crude guesses of amateur naturalists I xIV Preface. had previous experience. He very wisely said, that whether the hypothesis turned out to be a correct one or not, one thing was plain, that the amount of evidence I had to give in its support was not enough for the purpose. I left the matter therefore for the time alone, and promised myself to hunt for further evidence, when my next year’s holiday should come. But before that time came, this essay of Kerner made its appearance, rendering all further evidence unnecessary. He shows,’ by a mass of evidence which cannot but enforce con- viction, that a viscid stem or viscid calyx is only one amongst many contrivances, by which useless insects are excluded from the nectaries. The general result of his essay is to show, that, as the presence of nectar in a flower implies most surely cross-fertilisation by the agency of suitable animals, so also does it, with almost equal certainty, imply the presence of some or other contrivance by which that nectar shall be preserved from unsuitable ones. The simplicity of some of the contrivances, and the ingenuity of others, and the variety of methods by which the same end is attained, are most striking. And if the reader derive but half the pleasure that I have done from their study, he will feel grateful for having Kerner’s essay made readily accessible to him. THE EDITOR. October, 1878. CONTENTS. PreFaToRY LETTER, Epitor’s PREFACE, CHAP. I, Introductory Remarks, : - : Ii. Advantages which accrue to the Plant from bearing Flowers, and especially from certain Conformations of Parts of the Flower, III. Disadvantageous Influences and Attacks to which Flowers are exposed during Blossoming, . : IV. Means of Protection against those Injurious Influences and Attacks by which the Advantages which accrue to the Plant from bearing Flowers might be lost, A. Protective Appliances of the Leaves, in which are formed the Materials for the Flowers, B. Protective Appliances of the Flowers against Un- bidden Guests, 3 . ‘ 1. Protection from certain Animals ig the Bandai in the Flowers of Distasteful Substances, 2. Access to the Flowers Impeded by their Isolation” in Water, ‘i 3. Access to Flowers Lapieded, by Viseid Hench ‘ 4. Access to Flowers impeded by Prickles, 5. Access to Flowers impeded by Hairy Formations, PAGE Y vii 14 27 28 32 35 39 49 69 79 Xvi Contents. CHAP, 6. Access to Flowers impeded by Parts of the Plant, and especially Parts of the Flower, being bent, or dilated, or crowded together, 7. Temporary Suspension of the Functions of those Parts of the Flower which attract Insects, 8. Diversion of Visitors from the Flower, V. Concluding Remarks, Explanation of the Plates, Index of the Names of Plants, PAGE 98 130 135 140 152 159 CHAPTER I. INTRODUCTORY REMARKS. AmonG.the current phrases which the flood of litera- ture on the theory of natural selection has brought to the surface, there is scarcely-one more frequently used, and perhaps also misused, than “the preserva- tion of advantageous varieties.” These words do in truth sum up the whole theory, and there is nothing in the theory itself which can be made a reason- able ground of objection to them. The questions, however, which lie at the base of this theory remain, and will long remain, open to discussion—the ques- tion, that is, as to “the primary cause of individual varieties,” and further, the question as to “the ad- vantages derivable from any given peculiarity in an organism.” It appears to me to be urgently necessary that instead of indulging in oft-repeated, wide-branching, theo- retical discussions on the preservation of advantageous varieties, we should make the establishment of the 2 Flowers and thetr Unbidden Guests. facts our main object, should institute new experiments which may place the theory on a firmer basis, and should so solve the questions at issue by the experi- mental method. It cannot be denied that the founda- tions on which the theory at present rests were for the most part built up and obtained without known aim or purpose; that they consist of observations which were the result of accident rather than of definite intention, and which consequently present all the deficiencies which cling to chance or almost chance observations. The foundations, in short, are not such as can be relied on with perfect confidence, since most of the older observations leave room for doubt whether _ the observer even saw correctly, or whether, misled by some favourite hypothesis, he did not put down as an actual fact what was in reality no more than a con- jecture. The records, at any rate, of botanical literature are vitiated by a larger intermixture of falsity and fiction than any one would have thought possible in an experimental science. Observers have been eager to make their conclusions harmonise with the systematic descriptions and artificial separations of species to be found until quite recently, nay, even in the present day, in the leading phytographical works; and one finds in consequence the most absurd statements set forth as “experimental results.” Authors, who had neither the opportunity, nor moreover the requisite patience and determination, to test by experiment the Lnexact Observations. 3 pretended constancy or variability of species, declare with imposing certitude that, in laying down the boundaries between species, represented by them as systematic units, they were supported by results de- rived from the cultivation of plants under observation. Nay, even those who were in a position to proceed experimentally, did not hesitate, in their eagerness to support a preconceived idea, to issue as true coin fictitious observations. If to writers such as these we add those others who had no intention to deceive, but who rather deceived themselves in consequence of improper methods of research or carelessness of obser- vation, then indeed must all confidence in the state- ments of past writers fail us; and this the more, as we have no possible means of correctly separating the chaff from the wheat. Doubtless it is a very convenient plan to select, by your own standard, out of the chaos of existing state- ments, such as can serve to support a given hypothesis, 2 and to adopt these as “recognised facts ;” whilst you represent those which cannot be brought into harmony with it as the results of erroneous experimentation and of ignorant or inexact observation. But in the build- ing up of a science no good can come from such an arbitrary choice of materials. Considering, therefore, the utter uncertainty we are in as to the use of the older statements, there remains no other course open to us than to begin the whole work afresh, and so 4 Flowers and thety Unbidden Guests. patiently provide ourselves with fresh building-stones which shall be beyond suspicion. For the solution of the questions at issue, experiments and observations must be carried out with definite aim, so that all sub- jectivity may be as far as possible excluded, and so that each person may have it in his power to test their accuracy by repetition. As regards one of the questions mentioned above as underlying the theory of natural selection, namely, “ the primary cause of individual varieties or sub-species,” I shall have an opportunity this year in another place of publishing a series of observations bearing on the question. To the solution of the second question, namely, “ how far certain characters in the bearer are of advantage to the same,” the following pages may furnish a small contribution. CHAPTER II. ADVANTAGES WHICH ACCRUE TO THE PLANT FROM BEARING FLOWERS, AND ESPECIALLY FROM CERTAIN CONFORMATIONS OF PARTS OF THE FLOWER. ATTEMPTS have been made to arrange the characters of plants under two heads; those which give their bearers some definite advantage, and those which give none. The former are spoken of as physiological characters, the latter as morphological. It was thought incon- ceivable that any advantage could arise to a plant through having, for example, its leaves decussated in- stead of their being arranged quincuncially. This notion does not appear to me to be justified. That unadvan- tageous characters can appear in an individual, and in fact do appear not rarely, nay that deviations of forma- tion arise which are of direct disadvantage, is not indeed to be disputed ; and this fact is of wide signifi- cance in other questions. But just as certain is it, that the bearers of such unadvantageous characters never form the starting-point of a new species, but vanish, being driven from the scene by the bearers of advantageous characters. As regards the special case 6 Flowers and their Unbidden Guests. of a certain position of the leaf, the advantages it confers have been hitherto merely overlooked, or un- recognised. But the mere fact that a person does not at once perceive an advantage does not justify him in assuming that none exists; and any one who builds up a structure of hypotheses, the uncertainty of which is, moreover, increased by his own short-sightedness, must not be surprised to see his building forthwith tumble to the ground. * I hold the opinion that the position, direction, and shape, of the leaf is of just as great significance for the preservation of a species, as the form, colour, and smell of the flower ; and that no hair is meaningless, whether found on the cotyledon or the leaf, on the stem or the blossom. It is true that we know as yet very little as to the functional significance of the position and form of the several parts of plants. The very elements of their biology are as yet scarcely well made out. There is in science as elsewhere a changing fashion, and this gives to its teaching a preferential turn, now in one now in another direction. Most workers give their attention preferentially to that object which seems at the time most important; and among the branches of Botany - which during the last few decades have been shoved : aside, is unfortunately to be counted Biology ; that is to say, the determination of the functional significance of morphological characters, Flower-shapes and their Causes. 7 The part which hitherto has, in proportion to the rest, been most thoroughly studied is the significance of the endless varieties of form presented by the flower ; and the relations which exist between the parts of the flower and the animals which visit it have been especial objects of attention. In this inquiry there has been indisputably no lack of one-sided views and erroneous interpretations. With the common tendency of ex- plorers to confine themselves to the path indicated by some first successful experiments, men have tried to explain everything they possibly can by the relation between the shape of the flower and that of the animals that visit it; and, as was unavoidable, in so doing they have often overshot the mark, and by their one-sided mode of viewing the matter, have overlooked, entirely or in part, other definite advantages not thus to be explained. In my treatise on the means by which pollen is protected from premature dispersal, and from wet, I have pointed out a number of such errors, and have shown that many peculiarities of shape presented by flowers, which it was supposed were to be explained only by reference to the visits of insects, are in reality, either not at all or not exclusively concerned therewith. “It is manifest that those forms will be most likely to be preserved, and those structures to bé most frequently developed, which combine a plurality of advantages ; because thus the greatest possible results will be ob- 8 Flowers and their Unbidden Guests. tained with the least possible expenditure. And in fact it is rare that any part of a plant is so shaped as to be suitable for the attainment of but one end. Usually “two birds are hit with one stone,” nay, often three or more. It is precisely this varying accumulation of functions in parts morphologically identical, that determines the endless multiplicity of their forms. Itis not of course meant that herein lies the explanation of how that multiplicity originated, and what was its primary start. This question, however, as also the further one, why plants in general produce flowers and fruit, and do not remain limited to the vegetative mode of repro- duction, is outside our present inquiry. I purpose, in... the following pages, to do no more than set forth the functional significance of a number of parts that present a very great multifariousness in their develop- ment. But while I thus limit myself, I must start with the assumption that the sexual mode of repro- duction by periodic flowers and fruit is advantageous to every plant; and I may further intimate that, in my opinion, the advantage thus derived lies in its affording a possibility for the origination of new individuals differing in their external characters from their parents. As, moreover, the advantages which accrue from bearing flowers and fruit manifestly cannot be obtained . unless each several part fully performs its proper func- tion, it will not be inappropriate to bestow here some Functions of the Perianth. 9 words on the functions of the individual parts, and on the advantages presented by certain conformations of the perianth, the andreecium, and the gynecium. The main functions of the andreecium and gynecium are sufficiently well known. And how essential it is, that the generative cells in particular shall be per- mitted to develop themselves without external disturb- ance, scarcely needs mention. So also we may assume it to be admitted, that one of the offices of the perianth, at the time when the generative cells are being de- veloped, is to protect the parts in which this develop- ment occurs, that is to say, the andrcecium and gynecium, from external interference. At a later period it is also certainly one of the most important offices of the perianth to protect the coherent pollen, when discharged from the anthers, against premature wetting by rain or dew, against displacement by wind and by unbidden guests, as also against the destructive attacks of sundry animals. A still further and very frequent function of the perianth is to bring about autogamy,’ in those cases, that is, where the pollen from other flowers is not brought into contact with the stigma. And a fourth 1 TJ understand by autogamy the fecundation of a flower by the pollen from the andrecium of the same flower; by geitonogamy, the fecundation of a flower by pollen from other flowers on the same plant; by xenogamy, the fecundation of a flower by pollen from other plants. Geitonogamy and xenogamy may be classed together under the name allogamy. Such terms as “self-fer- tilisation” are to be avoided on account of their excessive indefi- niteness. c 10 Flowers and their Unbidden Guests. not less important function is to attract by the secre- tion of nectar, by odours perceptible afar, and by , colours contrasting vividly with the green of the leaves, such insects as may carry the pollen from one flower to another, and so bring about allogamy. Finally, the perianth has still another function, namely, to protect the nectar, which is not always secreted only at the base of the perianth, but often also in hollows of different parts of the andreecium or gynecium, or by : peculiar epiblastemes, sometimes of one sometimes of another of the floral whorls, or of the bottom of the flower, and which must be secured not only against injurious weather influences, but specially against the plundering of such insects as would visit the flower without conferring any advantage. Again the divisions of the perianth, in a more or less changed form, often act as a protection to the young fruits, which develop under their shelter. Often too they conduce to the dispersal of the seed, as when they form dry and membranous coverings which offer a relatively large surface to the wind (Trifolium badium), or when they adhere to roving animals either by viscidity (Plumbago, Linnea), or by hooklets (Marrubium), or when they are converted into fleshy pericarps which serve as food for animals. i 1[The fruit of Linnea borealis, as also the calyx of several species of Plumbago (P. micrantha, and rusea) are covered with glandular hairs. On the whole subject of special appliances for dispersal of seeds, consult the monograph of F. Hildebrand, Die Verbreitungsmittel der Pflanzen, Leipzig, 1873.—Eprror.] Nice Construction of Flowers. II These functions of the perianth are performed by it either quite alone, or, more frequently, in conjunction with special developments of the andreecium and gyn- ecium. Many flowers thus become very complicated machines, in which it is of the greatest importance that each part shall work with perfect accuracy, that not a piece of the apparatus shall be too long or too short, shall get damaged or out of place, or become unfitted for its office by the injurious effects of weather, or by the attacks of animals. If a leaf be gnawed by an insect, and in consequence suffer some loss of substance, or if a leaf undergo change in its shape and size through gall-producing insects, the performance of its function is thereby hampered, but, as a rule, not completely stopped. Quite other- wise is it with those floral organs which form a link in the chain of fertilisation. Here the smallest and most inconspicuous change in the size and shape of a part may render the function of the whole apparatus impossible. In Sternbergia and Colchicum, for example, when the erect flower closes, as it does in the evening, the pollen is pressed against the inner surface of the perianth, to which it adheres, and by its intermediation is conveyed to the stigma, which stands up above the anthers. This is brought about in the following manner :—The perianth increases in length during the blossoming period by intercalary growth ; and this lengthening is just such as to cause those spots on its inner surface, which, on 12 Flowers and their Unbidden Guests. the first day of flowering, had been smeared with pollen from the outwardly dehiscing anthers, to stand on the last day, at the final closing of the flower, on a level with the stigma. Again, take those species of Pedicu- laris, in which the upper petals form a beak-shaped tube. At the end of the blossoming period’ the dusty pollen gets into this little tube, and then, in conse- quence of an angular movement of the corolla which happens at this time, rolls upwards through the tube to the stigma, which stands close over the mouth, This as before results in autogamy. But the whole mechanism can onty be successful if the above-men-: tioned angular movement be of a definite strength, which again is only possible if the corolla be uninjured and undisturbed during the flowering period. In the blossoms of many Caryophyllaceze (which will be treated of more fully on a future page), the filaments of the stamens lengthen quite suddenly with the coming on of evening, The anthers are thus brought forward, above the tube of the corolla; they open, and, owing to the position they have now assumed, expose their pollen in such a situation that insects, attracted to the flowers by the nectar, must necessarily wipe it off, and, flying elsewhere, carry it to another flower on the same plant. If, at the time when the pollen is exposed in these 1[In the earlier period of flowering, Pedicularis has flowers most ingeniously adapted for cross-fertilisation ; cf. Pop. Science Rev., 1870, p. 45, where I have described it.—Eprror,] Flowers of Caryophyllacee. 13 plants, that is, in'the evening, the nectar should fail, then no insect would visit them, and the advantage of geitonogamy or xenogamy, brought about by their means, would be lost. The nectar, therefore, must be reserved for the evening, and special arrangements must be made by which other nectar-loving insects, which visit flowers at any time in the day, and which would steal the nectar without any advantage to the plant, may be kept off. These two examples will suffice to show that a definite function belongs even to the most inconspi- cuous modifications of the individual parts of flowers, and that the parts of flowers must be protected, far more even than the leaves, from injury and disturbance in the performance of their functions, if the advantages attached to flowering are to be attained. CHAPTER III. DISADVANTAGEOUS INFLUENCES AND ATTACKS TO WHICH FLOWERS ARE EXPOSED DURING BLOSSOMING. On the presumption, that to produce flowers is an advantage to plants, there is an antecedent probability that each plant will do so, and will go through the successive stages of the process. But owing to the unceasing interaction which exists between plants and the outer world—inorganic nature on the one hand, and the animal kingdom on the other—this flowering process must necessarily be exposed to many possible interferences; in the one case to frost, drought, rain, or similar injurious action of the elements; in the other to the attacks of herbivorous, and therefore flower- destroying, animals. As regards the latter, though the dangers from the larger grazing animals, Ruminants, Solipedes, etc., etc., are the more conspicuous, yet those incurred from the attacks of smaller kinds, if less apparent, are by no means less real; from snails, that is, and wood-lice and insects, and from these latter, both in their larval and in their final stages of development. Exclusion of Snails and Soft Insects. 15 Of the Gasteropods, the voracious Helicide are espe- cially dangerous and unwelcome visitors. They are, however, to be found, comparatively speaking, but rarely upon ‘the flowers, This is not because the perianth- leaves are distasteful to them, but because they can be kept off more easily than other uninvited guests. A simple group of bristles or prickles on any part of the plant that has to be traversed by the snail in order to get at the flower is enough to prevent its further ad- vance. It avoids most carefully.all contact between its _ soft, easily injured body and the points of a bristle or a prickle; and, if it.comes to a place so protected, it turns back at once, without any further attempt to overcome the difficulty. The same holds good for such insects as have soft bodies, and especially for numerous caterpillars, many of which would readily devour the perianth-leaves, or those which go to form the gynecium, if they were not debarred from access to the flower. I once also noticed that caterpillars sought out the just-opened tubular flowers of the garden Penta- stemon gentianoides, as a corner protected from wind and weather, therein made their webs, and underwent their transformation, whereby the reproductive pro- cesses were rendered impossible in the flowers in question. Probably in those places where the Penta- stemon grows wild, it is not exposed to such visitors. Nevertheless this observation is worth mentioning here, as it makes one suspect that the reason, why 16 Flowers and their Unbidden Guests. so many plants with bell-shaped or drooping flowers are provided with certain defensive contrivances, is that they may be able to keep off caterpillars from seeking in them a snug corner for their webs and transformations, and thus interfering with the fune- tions of the floral organs. Among the insects which have a soft outer skin, the wingless aphides require special notice. We usually find them in large numbers, and closely thronged, on the under side of the leaves, and on the stalks of the flowers and inflorescences. In flowers themselves they are only rarely to be met with, because there are special contrivances to prevent their access. If one transfers them to the perianth, or to other parts of the flower, they immediately thrust their rostrum into the juicy tissue, which shows that the petals would be perfectly acceptable to them. If placed on villous or tomentose, or upon bristly and prickly, leaves, they behave most awkwardly. They remain with their long legs hanging between the hairs, or injure themselves by their help- less movements on the sharp points of the trichomes and teeth of the leaves. Leaves, and groups of leaves, clothed with such defences, are therefore most carefully avoided by them, and this explains why the colonies of wingless aphides never advance farther up the stems and flower-stalks than the involucres and calyces,: when these are clothed with woolly or matted hairs, or with bristles and prickles. Chitinous Insects less eastly excluded. 17 In contrast with these soft-bodied animals are those insects that have a hard investment of chitin. These move with perfect ease even over very thorny and prickly stems and leaves. Only the terminal joints of their antenne are sensitive to the touch of hard points, their bodies and legs not being easily wounded. But it is precisely among these chitinous insects that many species are to be found whose visits would interfere very prejudicially with the functions of some or other parts of the flower. For in most cases the bodily dimensions of such creatures are not adapted to the general conformation of the flower; that is, their dimen- sions are so small that, in diving into the recesses of the flower for the nectar there secreted, they would touch neither the anthers nor the stigma. The result therefore of their visits would be that not only would the allurement, that is, the nectar, be taken away from those insects which possess bodies of a suitable size, and thus the advantage be lost which attaches to the visits of such invited guests, but that a further evil would ensue, inasmuch as these little unbidden guests would fill up the bottom of the flower, and so cause a mechanical hindrance, which would prevent the larger and welcome insects from pushing their trunks to the bottom of the nectaries. On the Muttenjoch, in the Gschnitz Valley, I once saw the small moth, Agrotis cuprea 8. V., which works not only by night but also most actively by day, 18 Flowers and their Unbidden Guests. sucking nectar from the blossoms of the Gentiana bavarica. It flitted from one blossom to another, but I was surprised to see that it passed over some of the numerous flowers, though growing close together, with- out attacking them. My first suspicion was that the nectar might have been lately carried off from these flowers by other insects, and that the reason why the moth did not insert its proboscis was, that it smelt! no nectar. But when I proceeded to open the flowers which had been thus passed over, I found that they | were not void of nectar, but that the several canals in the lower part of the corolla-tube which serve as carriers for the secretion were crammed full with small beetles (Anthobium excavatum). I noticed a similar fact in the Gentiana germanica at Trins in the Gschnitz Valley. Those flowers of this plant which were left unvisited by the humble-bees (Bombus mastrucatus and Psithyrus vestalis) always contained numerous speci- mens of Meligethes ewilis in their nectaries; and at a later period I had the opportunity of making similar observations on the flowers of Digitalis ambigua Murr. Cuphea platycentra, Eremurus tauricus, Iris tuberosa, and Primula glutinosa Wulf.” 1 In Gentiana bavarica L,, the nectar is stored at the bottom of the flower, where it cannot possibly be seen by flying insects, as the corolla-tube is closed by the large circular stigma (Plate I. fig. 37). The nectar must therefore in this, as in so many other cases, be smelt by the insects. 2 It is very probable that the species of Forficula also, which we frequently find working for days together in tubular flowers, so far Wingless Insects unwelcome. 19 The insects that are armed with a hard covering of chitin are usually winged, and then—supposing of course that they are vegetable feeders—generally reach the flowers by flying. Some of them, however, are wingless, and these, like the snails, etc., can only reach the flower by crawling and clambering over the axis and leaves. These wingless insects are unwelcome to the flowers under all circumstances; and their visits are disadvantageous even if they possess such bodily dimensions, that in pushing to the bottom of the flower they would rub against the pollen and the stigma in due succession. For such wingless insects, even when they leave a flower laden with pollen, cannot reach the flower of a second stem of the same species till after a long journey and a proportionally long space of time. A winged insect flies through the air from flower to flower with great rapidity, and often within a few minutes transports the pollen rubbed off from one flower to the stigma of a second, third, and fourth pretty distant one ; whereas a wingless insect must first return from the flower to the ground, and then creep or climb over the axis and leaves of a second stem. Now, putting on one side the loss of time which this entails, consider to what dangers the pollen carried by the insect is exposed in this transit! How easily it may be rubbed off on interfere with the floral functions, as that by their presence other insects, whose visits would be of use, are prevented from sucking the nectar. I possess, however, no definite observations on this point, 20 Flowers and their Unbidden Guests. the way by leaves, stems, or hairs; or wasted by wind and weather; and how improbable it also is, that a second flower to which the wingless insect, in spite of all the dangers by the way, still brings some of the pollen from the first flower, will be one exactly suitable for its reception. Flying insects in their search for nectar frequently confine themselves during their rapid visitation of successive flowers to the blossoms of one and the same species,’ whereas the wingless ones, after visiting and leaving a given flower, take no heed to reach another of the same species, but when back again on the ground are diverted by the least thing, and make the best of anything that turns up of use in their further progress. Herein we have a very probable explanation of the fact that flowers of very small size, flowers, that 1 For example, in a meadow at Trins, in the Gschnitz valley, I saw Bombus montanus Gerst. visiting only the inconspicuous flowers of Anthyllis alpestris Kit., whilst the numerous and far more strik- ing nectar-bearing flowers of Pedicularis Jacquini Koch. and Pedi- cularis incarnata Jacq. were passed over. Contrariwise, in another place, namely in a meadow in the Padail valley, I saw this same Bombus montanus buzzing from one Pedicularis flower to another, whilst passing over the intermixed Anthyllis alpestris. Neither in the one case nor in the other were the flowers in question filled with beetles ; and the nectar of the despised blossoms would have been perfectly easily accessible to the humble-bee. It appears that the humble-bees always devote themselves at one time to the plunder of one species of plant. [It is curious that a similar observation as to the habits of bees should have been made by Aristotle. ‘A bee,” he says (H. An. ix. 40), “‘on any one expedition, does not pass from one kind of plant to another, but confines itself to a single species, for instance to violets, and does not change until it has first returned to the hive.”— Ep1Tor. ] Ants especially unwelcome. 21 is, in which very tiny insects, in pressing forward to the nectariferous recesses, would necessarily come into due contact with the anthers and the stigma (eg. many Composite, Crucifere, Caryophyllacee, Saxifragez, Asperifoliz, etc.), are yet provided with defensive appli- ances which keep off such insects as are wingless, and only allow access to such as fly. Of all the wingless insects it is the widely dispersed ants that are the most unwelcome guests to flowers. And yet are they the very ones which have the greatest longing for the nectar, as numberless observations suf- ficiently show. Wherever there are aphides there one is sure to find ants seeking for the sweet fluid which these secrete. It is, moreover, well known that where- ever honey, sugar, saccharine fluids, dried fruits, etc., are placed without protection, there ants are to be found. As regards the nectar of flowers they are especially for- midable, inasmuch as they can smell! saccharine fluids 1 One of my colleagues at Innsbriick kept some dried pears on the ground-floor of a house directly contiguous to the garden, and to these the garden ants immediately found their way. As these uninvited guests could not be kept from the ground-floor, the pears were transferred to a room on the second story. But, notwith- standing this, the pears were beset by these same ants the very next day, and when investigation was made as to how the ants could possibly have got to the up-stairs room, it was found that they had made their way by a bell-wire which went from the garden into the second story and ran by the window of the room. The following communication from Gredler at Botzen is also not without interest. One of his colleagues had for months been in the habit of sprinkling pounded sugar on the sill of his window for a train of ants which passed in constant procession from the garden to the window.: 22 Flowers and their Unbidden Guests. even ata considerable distance, and moreover because they do not suspend their activity during the night, as I repeatedly noticed whilst making observations on the visitation of night-blowing flowers. But the reason why, notwithstanding this, wingless ants on the whole are found but rarely in flowers, is that there exists a large number of protective appliances by which the nectar is admirably protected against them. Should for once no such protective appliance be developed, or should it in any way be made useless or cease to act, should it in short in any way become possible for the ants to get at the nectar without harming themselves, then they forthwith appear in the flowers as guests. Of One day he took it into his head to put the pounded sugar into a vessel, which he fastened with a string to the transom of the window; and, in order that his long-petted insects might have information of the supply suspended above, a number of the same set of ants were placed with the sugar in the vessel. These busy creatures forthwith seized on the particles of sugar, and soon discovering the only way open to them, viz., up the string, over the transom and down the window-frame, rejoined their fellows on the sill, whence they could resume the oid route down the steep wall into the garden, Before long the route over the new track from the sill to the sugar, by the window-frame, transom, and string was completely established ; and so passed a day or two without anything new. Then one morning it was noticed that the ants were stopping at their old place, that is, the window-sill, and again getting sugar there. Not a single individual any longer traversed the path that led thence to the sugar above. This was not because the store above had been exhausted ; but because some dozen little fellows were working away vigorously and incessantly up aloft in the vessel, dragging the sugar crumbs to its edge, and throwing them down to their comrades below on the sill, a sill which with their limited range of vision they could not possibly see! (Gredler, Der Zoologische Garten, xv. 434.) Lxclusion of Ants. 23 this it is easy to convince oneself. Pluck, for instance, some of the flowers of Melianthus, or of any other plant in which, as in this, the nectariferous flowers, while growing in their natural position in the inflorescence, are admirably protected against the visits of ants, and having plucked them lay them on the ground. They are now unprotected, and in the shortest possible time they will be found swarming with ants. Another example is furnished by Phygelius capensis. Here the flowers are rich in nectar, all access to which is rendered impossible to ants during the period of flowering, by a method which I shall have to describe later on in detail. So soon, however, as the corolla detaches itself from the torus, the nectar, of which there is still an abundant store, becomes readily accessible, and ants (in the Botanical Gardens at Innsbriick abundance of Lasius niger) immediately crowd in and greedily lick it up. They can be allowed to do so at this period without ill result. For, now that the flowers are falling off, their nectar is useless, and no longer wanted to attract such flying insects as cause intercrossing. In this respect the case of Antirrhinum majus L. is also very instructive. Here the corolla remains closed so long as the stigma is unfecundated. Strong humble-bees can indeed force an opening and so bring about intercrossing; but ants are quite unable to squeeze in between the two closely compressed lips. But, when once the stigma has been covered with 24 Flowers and their Unbidden Guests. pollen, the tension of the corolla diminishes. The upper and lower lips separate from each other by a fissure, six mm. long on the sides and one mm. wide at the extremity ; and through this ants can now make their way and carry off the nectar, which has ceased to have any functional significance. I have convinced myself that, as a matter of fact, they do so. In bringing this chapter to an end, I may, in addition to the ants, make special mention of the physopodous thrips, which are found almost universally’ in flowers. These have been regarded by some writers as injurious, by others as welcome, visitors. In my opinion they may be either. Their visits are injurious if, after ran- sacking a flower and quitting it, their further progress does not bring them to a second flower of the same species, or only brings them to it after a long circuit; in short, if they behave like other wingless insects. ; oe On the other hand, their visits are profitable, if, after _. rifling one flower, they pass over with its pollen to another similar one; behave, that is, exactly like flying insects, and, like them, bring about intercrossing. As 1 I found them in the majority of flowers on the sea-coast and in the Puszten district in Hungary, no less than in the High Alps on the limits of eternal snow. They slip through the narrowest fissures, and are. not kept back by hairs, even when growing very closely together, so long as these hairs are not sticky. Even close above the nectariferous base of the spur of Centranthus ruber L, which could only be reached through a channel scarcely 0°8 mm. in width and 12 mm. in length, the inner side of which is covered all over with little hairs (see Plate ITI. figs. 97, 98), I still found thrips. Action of Thrips. 25 they usually act in the latter manner, the advantages they confer on plants far outbalance the disadvantages. Observations, moreover, that have been made render it very probable that in many cases, owing to certain arrangements presented by the plants, these insects can only pass from one flower, or one flower-head, to another, by a series of continuous jumps. It is with the greatest difficulty, for instance, that they can get across places beset with glandular hairs, and they avoid these most carefully. If placed experimentally on such places, they try to get clear by jumping, but usually are unable to set themselves free, and remain sticking to the hairs, where they soon perish. Thus the glandular hairs which are found so frequently upon peduncles, involucres, and calyces, as also upon certain parts of the corolla, and which we shall have to deal with hereafter as protecting flowers from many crawling animals, probably have reference also to the visits of thrips. Completely analogous to this action of the thrips is that of other larger insects. For here again it is the path and the mode of progression by which the flower is reached that determines whether the visit shall confer a benefit or an injury. There are, that is to say, numerous insects, among such as visit flowers and live upon them, which, if they come by flight, are bene- ficial visitors ; but which, if they were not to use their wings, but to gain access by climbing up the stalk i‘ ‘ 26 §©©Flowers and their Unbidden Guests. from below, would act injuriously. Nay, even insects whose sole method of access to a flower is by flight, may act sometimes advantageously and sometimes prejudicially, and, therefore, be sometimes welcome and sometimes unwelcome guests, according to the further course which they adopt within the flower itself. Of this, however, abundant evidence will be adduced later on. CHAPTER IV. MEANS OF PROTECTION AGAINST THOSE IN- . JURIOUS INFLUENCES AND ATTACKS BY WHICH THE ADVANTAGES WHICH ACCRUE TO THE PLANT FROM BEARING FLOWERS MIGHT BE LOST, THE disadvantageous influences and attacks to which flowers are exposed, and which have been set forth in the preceding pages, are compensated by the develop- ment of a large number of protective appliances which obviate, as far as possible, the mischiefs threatened. Some of these guard the flowers from injuries which they otherwise might suffer from wind, rain, and dew; while others ward off the attacks to which the blossoms are exposed from the animal world. As regards the latter, namely, the attacks of animals, it is, for the most part, in the flowers themselves that the protective appliances are to be found. In many cases, however, the axis and leaves are also protected, inasmuch as the destruction of these parts would endanger the formation of flowers. For the materials out of which the flowers are built up are formed, in all plants that have an axis, by the agency of that axis 28 Flowers and thetr Unbidden Guests. and of the leaves; and thus it is self-evident that any very extensive injury of these parts would also inter- fere with the perfect development of the blossom. Stem, therefore, and leaf-formations must, for a certain period and to a certain degree, be secured from the destructive attacks of animals, if for no other reason, yet in order that the material required for the forma- tion of flowers and fruit may be forthcoming. It will, therefore, I think, not be out of place to | devote a few pages to the methods by which leaves and stems are protected. A.—Protective Appliances of the Leaves, in which are "formed the Materials for the Flowers. In very many species of plants the foliage is pre- served from any extensive’ destruction by means of certain alkaloids and other chemical compounds con- tained in the cellular juice. The leaves of Datura and Solanum, of Aconitum, Helleborus, and Paeonia, of 1 Minor injuries which interfere but slightly with the function of the leaves cannot here be considered. The leaves of Adéropa belladonna L., for instance, may be eaten through and through by Haltica atrope All, and yet neither the development of the flowers nor the ripening of the fruit be in the least impeded. I do not mean to say that smaller animals than those referred to in the text may not do material damage to the foliage, or even destroy it completely. Their attacks, however, are not unprovided against, there being defensive appliances by which small creeping insects, snails, etc., are kept off from the leaves. Thus, to give a single example, the fimbriated cuffs constituting so many “ weels,” which are set round the petiole of Begonia manicata Vis., make it impos sible for a snail to crawl up and get at the juicy blades. Unpalatable Leaves, 29 Veratrum and Colchicum, Conium, Cyclamen, Aristo- lochia, Asarum, Sambucus ebulus, Asperula odorata, of all Crassulaceee, and of many other plants, are never touched by any ruminant. Some goats had one day unluckily got into the kitchen-garden of my summer residence, I noticed that they set to work vigorously at the cabbage, but passed over the leaves of the let- tuce. This led me to make the experiment of pre- senting leaves of Lactuca, Chelidonium, Papaver, and Euphorbia to different ruminants; when I soon found that they would rather go without food at all than submit to such a diet. So again the green leaves of the Aposeris feetida, which are full of milky juice—a plant which in the open spaces of the North-Alpine woods often covers the ground in masses—are never touched by the cattle which are driven to the forest pastures. The fact that many plants (Ballota, Lamium, Geranium Robertianum, Linaria vulgaris, Lepidiwm 1 This is the more remarkable, because lettuce leaves, as is well known, are readily eaten by numerous caterpillars. That which is sought for by one animal is frequently noxious to another ; nay it often happens that some chemical compound in a plant is a deadly poison to one animal, while to a second it is not only harmless but an object of eager search, The Haltica atrope All, for example mentioned in the preceding note, is not injured by the alkaloid contained in the leaf of the Deadly Nightshade, which to many animals is a violent poison. Thrushes also eat the berries of the Atropa without harm, whilst they are made ill by the Phytolacca "berries, which many other birds feed on without injury. [Rabbits also eat the Deadly Nightshade with apparent impunity. I have myself fed a rabbit for a week on this plant exclusively.—See Medical Times and Gazette, 1867.—Ep1toR.] 30 ©. Flowers and their Unbidden Guests. Draba, Plantago major, Juncus bufonius, etc.), which grow along the paths traversed by grazing animals, are able to maintain themselves and to develop their flowers and fruit without hindrance, in spite of their being exposed to the onslaught of these ruminants, has again no other explanation than the presence of certain chemical compounds in the cellular juice of their leaves which render them disagreeable to these animals. In many plants, again, the foliage is of thick and leathery consistence, and this also acts as a security against injury from ruminants. The wide tracts in the Alps which are seen covered with evergreen carpets and shrubby thickets of Azalea procumbens, Arctostaphylos uva urst, Dryas octopetala, Globularia cordifolia, Globu- laria nudicaulis, Daphne striata, Empetrum, Vaccinium vitis idaea, Rhododendron, and other characteristic plants, are avoided by sheep, as also by chamois, It is exceptional to find the leaves of these plants even mangled by grazing animals, and we never find them completely destroyed. Even grasses and sedges, when their leaves are un- pleasantly rigid, are carefully avoided by ruminants, Carex firma Host., which grows in thick masses on the wide flanks of the Alps, is never browsed. Nardus stricta L. again, and Juncus trifidus, which here and there in the Alpine regions form the fundamental part of the limited flora, are touched but exceptionally. That the leaves of many plants are also protected Prickly Leaves. at from attack by prickly appendages need scarcely be mentioned. In the district of Monte Baldo, as also in the mountainous regions lying to the east and stretch- ing out beyond the Etsch, a species of Festuca (Festuca alpestris Rom. et Schult.), is to be found very fre- quently growing in thick patches. This grass has stiff leaves which end in needle-shaped points, and when it grows in any abundance is burnt by the shepherds, because the grazing animals, in search- ing for other plants that grow with it, often get their nostrils pricked, and come home bleeding from their pasture-grounds, When it is the fully-developed leaves that require this kind of protection from grazing animals, one finds the thorns and prickles developed on the outer surface of the bushes and shrubs. When, on the other hand, it is the buds, the young unfolding leaves, or the bark, which must be insured against attack, or when the purpose is to keep off animals that creep up from the ground, it is on the stems that prickles are found, or it is the leaves or the stipules which are transformed into such organs, Many trees that are provided with thorns while young cease to develop such appendages when once they have attained a certain height. For their upper boughs, being above the reach of browsing animals, require no further protection for their leaves. In many cases, it is true, it is only a portion of the foliage that is protected in the above-mentioned ways 32 Flowers and their Unbidden Guests. from destruction by grazing animals; just such a portion in fact as is necessary in order that the further developmentary processes, which in the total absence of leaves would be completely arrested, may be carried on. Thus much being safe, the remainder is left to the tender mercies of animals. The very existence’ of herbivorous animals would plainly be impossible, were all the leaves of all plants rendered inaccessible to them or uneatable. It does not, however, come within the scope of this treatise to deal with these relations between plants and animals in detail. In making the above remarks I merely wish to indicate that those structural arrange- ments by which foliage is preserved, or rather in part preserved, from animals, are not without significance as regards the flowers; inasmuch as these can only develop themselves out of material which has first been fabricated by the leaves. B.—Protective Appliances of the Flowers against Unbidden Guests. If it be of importance to a plant to have some of its leaves protected from animals, of still greater importance is it that this shall be the case with its flowers. It was therefore to be expected that the flowers, which are constructed out of leaves, should be even better protected than the leaves themselves. Plants, whose flowers Welcome and Unwelcome Guests. 43 were not protected against the prejudicial attacks of animals, and yet attracted them by dainty and in- viting food, must sooner or later have been exter- minated, as they would have been overgrown and supplanted by others, the blossoms of which pos- sessed means of self-protection, and therefore stood at a decided advantage. Animals and plants however do not always stand in the relation of enemies and prey. On the contrary, it is well known that many plants derive great advantage from the visits of animals, nay, even sometimes from their very attacks, since often it is only by such agencies that the stigma can be properly fecundated. Consequently many flowers have special arrange- ments to allure insects to visit them. These allure- ments, it is true, are meant only for certain insects ; for many kinds, owing to the conformation of their bodies, would be of no use, but would rather be prejudicial, in the ways already mentioned. In relation to the vegetable world, or more correctly, in relation to each individual form of plant, animals may be divided into welcome invited guests, whose visits are of advantage, and into unwelcome uninvited guests, whose visits are prejudicial, or at least of no advantage. These invited and uninvited guests are of endless variety ; and corresponding to them, and of an almost 1 The benefits conferred by animals on plants in regard to the dispersal of seeds must be passed over here with this cursory allusion, 34 Flowers and their Unbidden Guests. inexhaustible multiplicity, are the allurements to visits and the means of protection against them. The diver- sity of the latter is so much the greater, inasmuch as the flowers of one kind of plant are not subject to the dis- advantageous attacks of only one kind of animal, but to the attacks of animals of the most various forms; great and small; winged or wingless; flying or creep- ing; biting or sucking; with a soft slimy skin, or armed with a layer of chitin and regardless of points and prickles ; some greedy after one part of the flower, some after another. On this account it happens very often that one single method of protection is insufficient, and that a plant, in order to preserve its flowers, allow them to blossom without disturbance, and let each part perform its right function, must be provided with two, three, or even more means of protection against animals of such various form and size. But in spite of this great complication, and in spite of the extraordinary variety of the arrangements which we are justified in considering as means of protec- tion against unbidden guests, we may perceive that certain types of defence, certain definite mechanisms | and arrangements, are always repeating themselves, and that it is quite possible in a descriptive account to bring order into this chaos, and to arrange the different means of protection into general groups. From this point of view it is curious to remark that one and the Direct and Indirect Protection. 35 same defensive appliance occurs sometimes on one part of a plant, sometimes on another; is sometimes developed on the stem, sometimes on the leaves, sometimes on the perianth; and that often plants, which having regard to other characters we should reckon as belong- ing to the most different families, are yet provided with identical means of protection. The defences against unwelcome guests may, accord- ing to my views, be divided into those which directly protect the flowers or some part of the same, and those which, though they do not directly prevent entrance into the flower, yet present an indirect hindrance. These indirect methods of defence are again of two kinds. In the one, at the time when the visit of the insect would be prejudicial, the organ which attracts it discontinues its function; in the other, formations are developed on the path by which the insect must approach the flower, which themselves furnish a suffi- ciency of dainty food, and so detain the visitor and prevent its further advance. In the succeeding pages I shall follow the order thus indicated. 1. Protection from certain Animals by the Secretion in the Flowers of Distasteful Substances. Any one who has bred butterflies, and for this pur- pose has fed caterpillars, knows that many of these latter eat the leaves of that plant which is their special 36 Flowers and their Unbidden Guests. food, whilst they would rather die of hunger than touch its blossoms. Herbivorous mammals also appear to have a distaste for flowers. Our cattle and sheep pass over the most beautiful blossoms, not only not attracted but apparently repelled by their sweet smell. Ihave many a time noticed cattle, whilst grazing in open glades, snuffle at the richly-scented blossom of Pyrola uniflora, Platanthera bifolia, Gymnadenia odoratissima, Convallaria majalis, and Viola odorata, but never have I seen them eat these flowers. So again in the autumn, when cattle are driven to tlieir pastures through meadows bright with countless blossoms of Colchicum, Parnassia, and Euphrasia, we can easily observe how, as they go, they snatch the sprouting leavesof grasses and of other plants from among the flowers, but never touch the flowers themselves.’ Again I have offered cattle fresh petals of honeysuckle, mallows, lilies, dahlias, and pinks, and they have let them lie untouched. In the valley of Non Ziegen I once noticed that the foliage of Cytisus alpinus was eaten with the greatest eagerness, while the thick clus- ters of blossoms were left unmolested. Another time, in a place where chamois had lately been feeding, I found the leaves of Migritella angustifolia, Phyteuma 1 [Mr. Darwin (Forms of Flowers, p. 6) quotes the following passage from his grandfather’s Loves of the Planis, written in 1790 :—“ The flowers or petals of plants are perhaps in general more acrid than their leaves; hence they are much seldomer eaten by insects.” —Eprror.] foliage eaten—Flowers left. 37 henisphaericum, Gaya simplex, Hedysarum obscurum, Trifolium alpinum, Ranunculus glacialis and Senecio doronicum, partly bitten off, but the flowers all left un- injured. Round the herdsmen’s buts one often sees great bush-like plants of Senecio cordatus, the foliage of which has been largely attacked by cows, sheep, and goats, whilst the flower-stems have been left intact. So along the roads where the cattle have gone to pasture, one may notice how the leaves of yarrow, the large flowered campanula, scabious, mullein, and similar plants, have been eaten off, while the greater part of their blossoms have been left unhurt. Parasitical plants and saprophytes, which have no green leaves, such as Orobanche, Neottia, Monotropa, Cuscuta, and Lathreea, are never touched by grazing animals. Many similar instances might be added. A curious fact may here be noticed. In cases where the flowers are so intermixed with the leaves, or so close to them, that destruction of the one involves destruction of the other, the leaves even are avoided by the animals. For example, the