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- Herausgeber: Booksell-Verlag
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
In "Darwinism stated by Darwin himself," Charles Darwin articulates the foundational concepts of his groundbreaking theory of evolution, emphasizing natural selection as the primary mechanism of gradual species change. The book is marked by a meticulous literary style that blends scientific rigor with accessible language, allowing both scholars and lay readers to engage with profound ideas. Contextually, this work emerges during the late 19th century, a period rife with scientific exploration and intellectual upheaval, marking a shift in understanding life sciences and challenging established beliefs about creation and species origin. Charles Darwin, an esteemed naturalist and biologist, meticulously observed diverse biological phenomena during his extensive voyages, most notably on the HMS Beagle. His exposure to various ecosystems and species diversity provided the impetus for formulating his theories on evolution. The synthesis of his empirical observations and introspective analysis culminated in this work, aiming to convey complex ideologies with clarity and precision. I wholeheartedly recommend "Darwinism stated by Darwin himself" to readers interested in the intersections of science, philosophy, and history. This essential text not only elucidates the principles of evolution but also sparks a deeper understanding of humanity's place within the natural world, making it a pivotal addition to any thoughtful reader's library. In this enriched edition, we have carefully created added value for your reading experience: - A succinct Introduction situates the work's timeless appeal and themes. - The Synopsis outlines the central plot, highlighting key developments without spoiling critical twists. - A detailed Historical Context immerses you in the era's events and influences that shaped the writing. - An Author Biography reveals milestones in the author's life, illuminating the personal insights behind the text. - A thorough Analysis dissects symbols, motifs, and character arcs to unearth underlying meanings. - Reflection questions prompt you to engage personally with the work's messages, connecting them to modern life. - Hand‐picked Memorable Quotes shine a spotlight on moments of literary brilliance. - Interactive footnotes clarify unusual references, historical allusions, and archaic phrases for an effortless, more informed read.
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Veröffentlichungsjahr: 2023
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Darwinism stated by Darwin himself
Table of Contents
PREFACE.
While these selections can not but be useful to those who are perfectly familiar with the writings of Darwin, they are designed especially for those who know little, or nothing, about his line of research and argument, and yet would like to obtain a general idea of it in a form which shall be at once authentic, brief, and inexpensive.
This volume contains, of course, only an outline of the contents of the twelve volumes from which it is compiled, and for which it is by no means intended as a substitute. It will, on the contrary, we should hope, create an appetite which can be satisfied only by a careful reading of the works themselves.
Darwin’s repetitions, necessitated by his method of investigation and publication, and his unexampled candor in controversy, have been something of an embarrassment in the classification of these passages; so that we have been obliged in some instances to sacrifice continuity to perspicuity. But, as one object of this book is to correct misrepresentations by giving Darwin’s views in his own language, some of his own repetitions must be given also, in order to leave no doubt as to precisely what he said and did not say. It will probably be a long while before the dispute over the theory that he advocated will cease, but there is certainly no excuse for a difference of opinion with regard to the language that he used, and the meaning he attached to it. That language and that meaning will be found in these pages. Darwinism stated by its opponents is one thing, Darwinism stated by Darwin himself will be found to be quite another thing, for, to use his own exclamation, “great is the power of steady misrepresentation!”
The order followed in the arrangement of these extracts is not that of the books, but the one naturally suggested by our plan, which is designed to conduct the reader through the vegetable up to the animal kingdom, and up from the lowest to the highest animal, man, “the wonder and glory of the universe.”
The references are to the American edition of Darwin’s works published by D. Appleton & Co., New York.
It is no part of our purpose to discuss the theory expounded here, but we can not refrain from joining in the general expression of admiration for its illustrious expounder. Lord Derby says, “He was one of half a dozen men of this century who will be remembered a century hence”; and yet his friends were “more impressed with the dignified simplicity of his nature than by the great work he had done.” Professor Huxley compares him to Socrates in wisdom and humility; and there could be no better authority than Mr. A.R. Wallace for the statement that “there are none to stand beside him as equals in the whole domain of science.” He has been extolled, since his death, by a host of religious leaders in press and pulpit (some of whose utterances will be found on another page), and we concur with them in the opinion that science never had a champion whose temper and behavior were more nearly in accord with the practical injunctions of the Christian religion. Whatever we or any one may think of Darwin’s scientific theories, no one can gainsay the value of his personal example, and few can be so prejudiced as to resist the fascination that will always be felt at the mention of his name.
New York, February 1, 1884.
INTRODUCTORY PASSAGES QUOTED BY DARWIN IN HIS “ORIGIN OF SPECIES.”
“But with regard to the material world, we can at least go so far as this—we can perceive that events are brought about not by insulated interpositions of divine power, exerted in each particular case, but by the establishment of general laws.”—Whewell: Bridgewater Treatise.
“The only distinct meaning of the word ‘natural’ is stated, fixed, or settled; since what is natural as much requires and presupposes an intelligent agent to render it so, i. e., to effect it continually or at stated times, as what is supernatural or miraculous does to effect it for once.”—Butler: Analogy of Revealed Religion.
“To conclude, therefore, let no man out of a weak conceit of sobriety, or an ill-applied moderation, think or maintain, that a man can search too far or be too well studied in the book of God’s word, or in the book of God’s works; divinity or philosophy; but rather let men endeavor an endless progress or proficience in both.”—Bacon: Advancement of Learning.
DARWIN AND HIS THEORIES FROM A RELIGIOUS POINT OF VIEW.
“Surely in such a man lived that true charity which is the very essence of the true spirit of Christ.”—Canon Prothero.
“The moral lesson of his life is perhaps even more valuable than is the grand discovery which he has stamped on the world’s history.”—The Observer (London).
“Darwin’s writings may be searched in vain for an irreverent or unbelieving word.”—The Church Review.
“The doctrine of evolution with which Darwin’s name would always be associated lent itself at least as readily to the old promise of God as to more modern but less complete explanations of the universe.”—Canon Barry.
“The fundamental doctrine of the theist is left precisely as it was. The belief in the great Creator and Ruler of the Universe is, as we have seen, confessed by the author of these doctrines. The grounds remain untouched of faith in the personal Deity who is in intimate relation with individual souls, who is their guide and helper in life, and who can be trusted in regard to the great hereafter.”—The Church Quarterly Review.
“It appears impossible to overrate the gain we have won in the stupendous majesty of this (Darwin’s) idea of the Creator and creation.”—Sunday-School Chronicle.
“It is certain that Mr. Darwin’s books contain a marvelous store of patiently accumulated and most interesting facts. Those facts seem to point in the direction of the belief that the Great Spirit of the Universe has wrought slowly and with infinite patience, through innumerable ages, rather than by abrupt intervention and by means of great catastrophes, in the production of the results, in the animate and inanimate world, which now offer to the student of nature boundless scope for observation and inquiry.”—The Christian World.
“Let us see, in the funeral honors paid within these holy precincts to our greatest naturalist, a happy trophy of the reconciliation between faith and science.”—The Guardian.
“That there is some truth in the theory of evolution, however, most scientists, including those of Christian faith, believe, and Mr. Darwin certainly has done much to make the facts plain; but no scientific principle established by him ever has undermined any truth of the Gospel.”—The Congregationalist.
“Christian believers are found among the ranks of evolutionists without apparent prejudice to their faith. Professor Mivart, the zoölogist; Professor Asa Gray, the botanist; Professor Le Conte and Professor Winchell, the geologists, may be named as among these.”—The Presbyterian.
“In all his simple and noble life Mr. Darwin was influenced by the profoundly religious conviction that nothing was beneath the earnest study of man which had been worthy of the mighty hand of God.”—Canon Farrar.
“He has not one word to say against religion; ... by-and-by it may be seen that he has done much to put religious faith as well as scientific knowledge on a higher plane.”—Independent.
“A celebrated author and divine has written to me that ‘he has gradually learned to see that it is just as noble a conception of the Deity to believe that he created a few original forms capable of self-development into other and needful forms, as to believe that he required a fresh act of creation to supply the voids caused by the action of his laws.’”—Origin of Species, page422.
“I am at the head of a college where to declare against it [evolution] would perplex my best students. They would ask me which to give up, science or the Bible.... It is but the evolution of Genesis when each ‘brings forth after its kind.’ Science tells the same story. But what is the limit of the fixedness of the law? I believe that the evolution of new species is a question in science, and not of religion. It should be left to scientific men.”—President McCosh.
DARWINISMSTATED BY DARWIN HIMSELF.
I.THE MOVEMENTS AND HABITS OF PLANTS.
The most widely prevalent movement is essentially of the same nature as that of the stem of a climbing plant, which bends successively to all points of the compass, so that the tip revolves. This movement has been called by Sachs “revolving nutation”; but we have found it much more convenient to use the terms circumnutation and circumnutate. As we shall have to say much about this movement, it will be useful here briefly to describe its nature. If we observe a circumnutating stem, which happens at the time to be bent, we will say toward the north, it will be found gradually to bend more and more easterly, until it faces the east; and so onward to the south, then to the west, and back again to the north. If the movement had been quite regular, the apex would have described a circle, or rather, as the stem is always growing upward, a circular spiral. But it generally describes irregular elliptical or oval figures; for the apex, after pointing in any one direction, commonly moves back to the opposite side, not, however, returning along the same line. Afterward other irregular ellipses or ovals are successively described, with their longer axes directed to different points of the compass. While describing such figures, the apex often travels in a zigzag line, or makes small subordinate loops or triangles. In the case of leaves the ellipses are generally narrow.
Even the stems of seedlings before they have broken through the ground, as well as their buried radicles, circumnutate, as far as the pressure of the surrounding earth permits. In this universally present movement we have the basis or groundwork for the acquirement, according to the requirements of the plant, of the most diversified movements.
THE MOVEMENT OF PLANTS IN RELATION TO THEIR WANTS.
The most interesting point in the natural history of climbing plants is the various kinds of movement which they display in manifest relation to their wants. The most different organs—stems, branches, flower-peduncles, petioles, mid-ribs of the leaf and leaflets, and apparently aërial roots—all possess this power.
1. The first action of a tendril is to place itself in a proper position. For instance, the tendril of Cobæa first rises vertically up, with its branches divergent and with the terminal hooks turned outward; the young shoot at the extremity of the stem is at the same time bent to one side, so as to be out of the way. The young leaves of clematis, on the other hand, prepare for action by temporarily curving themselves downward, so as to serve as grapnels.
2. If a twining plant or a tendril gets by any accident into an inclined position, it soon bends upward, though secluded from the light. The guiding stimulus no doubt is the attraction of gravity, as Andrew Knight showed to be the case with germinating plants. If a shoot of any ordinary plant be placed in an inclined position in a glass of water in the dark, the extremity will, in a few hours, bend upward; and, if the position of the shoot be then reversed, the downward-bent shoot reverses its curvature; but if the stolon of a strawberry, which has no tendency to grow upward, be thus treated, it will curve downward in the direction of, instead of in opposition to, the force of gravity. As with the strawberry, so it is generally with the twining shoots of the Hibbertia dentata, which climbs laterally from bush to bush; for these shoots, if placed in a position inclined downward, show little and sometimes no tendency to curve upward.
3. Climbing plants, like other plants, bend toward the light by a movement closely analogous to the incurvation which causes them to revolve, so that their revolving movement is often accelerated or retarded in traveling to or from the light. On the other hand, in a few instances tendrils bend toward the dark.
4. We have the spontaneous revolving movement which is independent of any outward stimulus, but is contingent on the youth of the part, and on vigorous health; and this again, of course, depends on a proper temperature and other favorable conditions of life.
5. Tendrils, whatever their homological nature may be, and the petioles or tips of the leaves of leaf-climbers, and apparently certain roots, all have the power of movement when touched, and bend quickly toward the touched side. Extremely slight pressure often suffices. If the pressure be not permanent, the part in question straightens itself and is again ready to bend on being touched.
6. Tendrils, soon after clasping a support, but not after a mere temporary curvature, contract spirally. If they have not come into contact with any object, they ultimately contract spirally, after ceasing to revolve; but in this case the movement is useless, and occurs only after a considerable lapse of time.
With respect to the means by which these various movements are effected, there can be little doubt, from the researches of Sachs and H. de Vries, that they are due to unequal growth; but, from the reasons already assigned, I can not believe that this explanation applies to the rapid movements from a delicate touch.
Finally, climbing plants are sufficiently numerous to form a conspicuous feature in the vegetable kingdom, more especially in tropical forests. America, which so abounds with arboreal animals, as Mr. Bates remarks, likewise abounds, according to Mohl and Palm, with climbing plants; and, of the tendril-bearing plants examined by me, the highest developed kinds are natives of this grand continent, namely, the several species of Bignonia, Eccremocarpus, Cobæa, and Ampelopsis. But even in the thickets of our temperate regions the number of climbing species and individuals is considerable, as will be found by counting them.
THE POWER OF MOVEMENT IN ANIMAL AND PLANT COMPARED.
It has often been vaguely asserted that plants are distinguished from animals by not having the power of movement. It should rather be said that plants acquire and display this power only when it is of some advantage to them; this being of comparatively rare occurrence, as they are affixed to the ground, and food is brought to them by the air and rain. We see how high in the scale of organization a plant may rise, when we look at one of the more perfect tendril-bearers. It first places its tendrils ready for action, as a polypus places its tentacula. If the tendril be displaced, it is acted on by the force of gravity and rights itself. It is acted on by the light, and bends toward or from it, or disregards it, whichever maybe most advantageous. During several days the tendrils or internodes, or both, spontaneously revolve with a steady motion. The tendril strikes some object, and quickly curls round and firmly grasps it. In the course of some hours it contracts into a spire, dragging up the stem, and forming an excellent spring. All movements now cease. By growth the tissues soon become wonderfully strong and durable. The tendril has done its work, and has done it in an admirable manner.
It is impossible not to be struck with the resemblance between the foregoing movements of plants and many of the actions performed unconsciously by the lower animals. With plants an astonishingly small stimulus suffices; and even with allied plants one may be highly sensitive to the slightest continued pressure, and another highly sensitive to a slight momentary touch. The habit of moving at certain periods is inherited both by plants and animals; and several other points of similitude have been specified. But the most striking resemblance is the localization of their sensitiveness, and the transmission of an influence from the excited part to another which consequently moves. Yet plants do not, of course, possess nerves or a central nervous system; and we may infer that with animals such structures serve only for the more perfect transmission of impressions, and for the more complete intercommunication of the several parts.
ADVANTAGES OF CROSS-FERTILIZATION.
There are two important conclusions which may be deduced from my observations: 1. That the advantages of cross-fertilization do not follow from some mysterious virtue in the mere union of two distinct individuals, but from such individuals having been subjected during previous generations to different conditions, or to their having varied in a manner commonly called spontaneous, so that in either case their sexual elements have been in some degree differentiated; and, 2. That the injury from self-fertilization follows from the want of such differentiation in the sexual elements. These two propositions are fully established by my experiments. Thus, when plants of the Ipomœa and of the Mimulus, which had been self-fertilized for the seven previous generations, and had been kept all the time under the same conditions, were intercrossed one with another, the offspring did not profit in the least by the cross.
The curious cases of plants which can fertilize and be fertilized by any other individual of the same species, but are altogether sterile with their own pollen, become intelligible, if the view here propounded is correct, namely, that the individuals of the same species growing in a state of nature near together have not really been subjected during several previous generations to quite the same conditions.
POTENCY OF THE SEXUAL ELEMENTS IN PLANTS.
It is obvious that the exposure of two sets of plants during several generations to different conditions can lead to no beneficial results, as far as crossing is concerned, unless their sexual elements are thus affected. That every organism is acted on to a certain extent by a change in its environment will not, I presume, be disputed. It is hardly necessary to advance evidence on this head; we can perceive the difference between individual plants of the same species which have grown in somewhat more shady or sunny, dry or damp places. Plants which have been propagated for some generations under different climates or at different seasons of the year transmit different constitutions to their seedlings. Under such circumstances, the chemical constitution of their fluids and the nature of their tissues are often modified. Many other such facts could be adduced. In short, every alteration in the function of a part is probably connected with some corresponding, though often quite imperceptible, change in structure or composition.
Whatever affects an organism in any way, likewise tends to act on its sexual elements. We see this in the inheritance of newly acquired modifications, such as those from the increased use or disuse of a part, and even from mutilations if followed by disease. We have abundant evidence how susceptible the reproductive system is to changed conditions, in the many instances of animals rendered sterile by confinement; so that they will not unite, or, if they unite, do not produce offspring, though the confinement may be far from close; and of plants rendered sterile by cultivation. But hardly any cases afford more striking evidence how powerfully a change in the conditions of life acts on the sexual elements than those already given, of plants which are completely self-sterile in one country, and, when brought to another, yield, even in the first generation, a fair supply of self-fertilized seeds.
But it may be said, granting that changed conditions act on the sexual elements, How can two or more plants growing close together, either in their native country or in a garden, be differently acted on, inasmuch as they appear to be exposed to exactly the same conditions?
EXPERIMENTS IN CROSSING.
In my experiments with Digitalis purpurea, some flowers on a wild plant were self-fertilized, and others were crossed with pollen from another plant growing within two or three feet distance. The crossed and self-fertilized plants raised from the seeds thus obtained produced flower-stems in number as 100 to 47, and in average height as 100 to 70. Therefore, the cross between these two plants was highly beneficial; but how could their sexual elements have been differentiated by exposure to different conditions? If the progenitors of the two plants had lived on the same spot during the last score of generations, and had never been crossed with any plant beyond the distance of a few feet, in all probability their offspring would have been reduced to the same state as some of the plants in my experiments—such as the intercrossed plants of the ninth generation of Ipomœa, or the self-fertilized plants of the eighth generation of Mimulus, or the offspring from flowers on the same plant; and in this case a cross between the two plants of Digitalis would have done no good. But seeds are often widely dispersed by natural means, and one of the above two plants, or one of their ancestors, may have come from a distance, from a more shady or sunny, dry or moist place, or from a different kind of soil containing other organic seeds or inorganic matter.
THE STRUGGLE FOR EXISTENCE AMONG SEEDS.
Seeds often lie dormant for several years in the ground, and germinate when brought near the surface by any means, as by burrowing animals. They would probably be affected by the mere circumstance of having long lain dormant; for gardeners believe that the production of double flowers, and of fruit, is thus influenced. Seeds, moreover, which were matured during different seasons will have been subjected during the whole course of their development to different degrees of heat and moisture.
It has been shown that pollen is often carried by insects to a considerable distance from plant to plant. Therefore, one of the parents or ancestors of our two plants of Digitalis may have been crossed by a distant plant growing under somewhat different conditions. Plants thus crossed often produce an unusually large number of seeds; a striking instance of this fact is afforded by the Bignonia, which was fertilized by Fritz Müller with pollen from some adjoining plants and set hardly any seed, but, when fertilized with pollen from a distant plant, was highly fertile. Seedlings from a cross of this kind grow with great vigor, and transmit their vigor to their descendants. These, therefore, in the struggle for life, will generally beat and exterminate the seedlings from plants which have long grown near together under the same conditions, and will thus tend to spread.
PRACTICAL APPLICATION OF THESE VIEWS.
Under a practical point of view, agriculturists and horticulturists may learn something from the conclusions at which we have arrived. Firstly, we see that the injury from the close breeding of animals and from the self-fertilization of plants does not necessarily depend on any tendency to disease or weakness of constitution common to the related parents, and only indirectly on their relationship, in so far as they are apt to resemble each other in all respects, including their sexual nature. And, secondly, that the advantages of cross-fertilization depend on the sexual elements of the parents having become in some degree differentiated by the exposure of their progenitors to different conditions, or from their having intercrossed with individuals thus exposed; or, lastly, from what we call in our ignorance spontaneous variation. He therefore who wishes to pair closely related animals ought to keep them under conditions as different as possible.
As some kinds of plants suffer much more from self-fertilization than do others, so it probably is with animals from too close interbreeding. The effects of close interbreeding on animals, judging again from plants, would be deterioration in general vigor, including fertility, with no necessary loss of excellence of form; and this seems to be the usual result.
It is a common practice with horticulturists to obtain seeds from another place having a very different soil, so as to avoid raising plants for a long succession of generations under the same conditions; but, with all the species which freely intercross by the aid of insects or the wind, it would be an incomparably better plan to obtain seeds of the required variety, which had been raised for some generations under as different conditions as possible, and sow them in alternate rows with seeds matured in the old garden. The two stocks would then intercross, with a thorough blending of their whole organizations, and with no loss of purity to the variety; and this would yield far more favorable results than a mere exchange of seeds. We have seen in my experiments how wonderfully the offspring profited in height, weight, hardiness, and fertility, by crosses of this kind. For instance, plants of Ipomœa thus crossed were to the intercrossed plants of the same stock, with which they grew in competition, as 100 to 78 in height, and as 100 to 51 in fertility; and plants of Eschscholtzia similarly compared were as 100 to 45 in fertility. In comparison with self-fertilized plants the results are still more striking; thus cabbages derived from a cross with a fresh stock were to the self-fertilized as 100 to 22 in weight.
Florists may learn, from the four cases which have been fully described, that they have the power of fixing each fleeting variety of color, if they will fertilize the flowers of the desired kind with their own pollen for half a dozen generations, and grow the seedlings under the same conditions. But a cross with any other individual of the same variety must be carefully prevented, as each has its own peculiar constitution. After a dozen generations of self-fertilization, it is probable that the new variety would remain constant even if grown under somewhat different conditions; and there would no longer be any necessity to guard against intercrosses between the individuals of the same variety.
MARRIAGES OF FIRST COUSINS.
With respect to mankind, my son George has endeavored to discover by a statistical investigation whether the marriages of first cousins are at all injurious, although this is a degree of relationship which would not be objected to in our domestic animals; and he has come to the conclusion from his own researches, and those of Dr. Mitchell, that the evidence as to any evil thus caused is conflicting, but on the whole points to its being very small. From the facts given in this volume we may infer that with mankind the marriages of nearly related persons, some of whose parents and ancestors had lived under very different conditions, would be much less injurious than that of persons who had always lived in the same place and followed the same habits of life. Nor can I see reason to doubt that the widely different habits of life of men and women in civilized nations, especially among the upper classes, would tend to counterbalance any evil from marriages between healthy and somewhat closely related persons.
DEVELOPMENT OF THE TWO SEXES IN PLANTS.
Under a theoretical point of view it is some gain to science to know that numberless structures in hermaphrodite plants, and probably in hermaphrodite animals, are special adaptations for securing an occasional cross between two individuals; and that the advantages from such a cross depend altogether on the beings which are united, or their progenitors, having had their sexual elements somewhat differentiated, so that the embryo is benefited in the same manner as is a mature plant or animal by a slight change in its conditions of life, although in a much higher degree.
Another and more important result may be deduced from my observations. Eggs and seeds are highly serviceable as a means of dissemination, but we now know that fertile eggs can be produced without the aid of the male. There are also many other methods by which organisms can be propagated asexually. Why then have the two sexes been developed, and why do males exist which can not themselves produce offspring? The answer lies, as I can hardly doubt, in the great good which is derived from the fusion of two somewhat differentiated individuals; and with the exception of the lowest organisms this is possible only by means of the sexual elements, these consisting of cells separated from the body, containing the germs of every part, and capable of being fused completely together.
It has been shown in the present volume that the offspring from the union of two distinct individuals, especially if their progenitors have been subjected to very different conditions, have an immense advantage in height, weight, constitutional vigor and fertility over the self-fertilized offspring from one of the same parents. And this fact is amply sufficient to account for the development of the sexual elements, that is, for the genesis of the two sexes.
It is a different question why the two sexes are sometimes combined in the same individual, and are sometimes separated. As with many of the lowest plants and animals the conjugation of two individuals, which are either quite similar or in some degree different is a common phenomenon, it seems probable, as remarked in the last chapter, that the sexes were primordially separate. The individual which receives the contents of the other, may be called the female; and the other, which is often smaller and more locomotive, may be called the male; though these sexual names ought hardly to be applied as long as the whole contents of the two forms are blended into one. The object gained by the two sexes becoming united in the same hermaphrodite form probably is to allow of occasional or frequent self-fertilization, so as to insure the propagation of the species, more especially in the case of organisms affixed for life to the same spot. There does not seem to be any great difficulty in understanding how an organism, formed by the conjugation of two individuals which represented the two incipient sexes, might have given rise by budding first to a monœcious and then to an hermaphrodite form; and in the case of animals even without budding to an hermaphrodite form, for the bilateral structure of animals perhaps indicates that they were aboriginally formed by the fusion of two individuals.
WHY THE SEXES HAVE BEEN RESEPARATED.
It is a more difficult problem why some plants, and apparently all the higher animals, after becoming hermaphrodites, have since had their sexes reseparated. This separation has been attributed by some naturalists to the advantages which follow from a division of physiological labor. The principle is intelligible when the same organ has to perform at the same time diverse functions; but it is not obvious why the male and female glands, when placed in different parts of the same compound or simple individual, should not perform their functions equally well as when placed in two distinct individuals. In some instances the sexes may have been reseparated for the sake of preventing too frequent self-fertilization; but this explanation does not seem probable, as the same end might have been gained by other and simpler means, for instance, dichogamy. It may be that the production of the male and female reproductive elements and the maturation of the ovules was too great a strain and expenditure of vital force for a single individual to withstand, if endowed with a highly complex organization; and that at the same time there was no need for all the individuals to produce young, and consequently that no injury, on the contrary, good, resulted from half of them, or the males, failing to produce offspring.
COMPARATIVE FERTILITY OF MALE AND FEMALE PLANTS.
Thirteen bushes (of the spindle-tree) growing near one another in a hedge consisted of eight females quite destitute of pollen, and of five hermaphrodites with well-developed anthers. In the autumn the eight females were well covered with fruit, excepting one which bore only a moderate number. Of the five hermaphrodites, one bore a dozen or two fruits, and the remaining four bushes several dozen; but their number was as nothing compared with those on the female bushes, for a single branch, between two and three feet in length, from one of the latter, yielded more than any one of the hermaphrodite bushes. The difference in the amount of fruit produced by the two sets of bushes is all the more striking, as from the sketches above given it is obvious that the stigmas of the polleniferous flowers can hardly fail to receive their own pollen; while the fertilization of the female flowers depends on pollen being brought to them by flies and the smaller Hymenoptera, which are far from being such efficient carriers as bees.
I now determined to observe more carefully during successive seasons some bushes growing in another place about a mile distant. As the female bushes were so highly productive, I marked only two of them with the letters A and B, and five polleniferous bushes with the letters C to G. I may premise that the year 1865 was highly favorable for the fruiting of all the bushes, especially for the polleniferous ones, some of which were quite barren, except under such favorable conditions. The season of 1864 was unfavorable. In 1863 the female A produced “some fruit”; in 1864 only nine; and in 1865 ninety-seven fruit. The female B in 1863 was “covered with fruit”; in 1864 it bore twenty-eight; and in 1865 “innumerable very fine fruits.” I may add that three other female trees growing close by were observed, but only during 1863, and they then bore abundantly. With respect to the polleniferous bushes, the one marked C did not bear a single fruit during the years 1863 and 1864, but during 1865 it produced no less than ninety-two fruit, which, however, were very poor. I selected one of the finest branches with fifteen fruit, and these contained twenty seeds, or on an average 1·33 per fruit. I then took by hazard fifteen fruit from an adjoining female bush, and these contained forty-three seeds; that is, more than twice as many, or on an average 2·86 per fruit. Many of the fruits from the female bushes included four seeds, and only one had a single seed; whereas, not one fruit from the polleniferous bushes contained four seeds. Moreover, when the two lots of seeds were compared, it was manifest that those from the female bushes were the larger. The second polleniferous bush, D, bore in 1863 about two dozen fruit, in 1864 only three very poor fruit, each containing a single seed; and in 1865, twenty equally poor fruit. Lastly, the three polleniferous bushes, E, F, and G, did not produce a single fruit during the three years 1863, 1864, and 1865.
EFFECT OF CLIMATE ON REPRODUCTION.
A tendency to the separation of the sexes in the cultivated strawberry seems to be much more strongly marked in the United States than in Europe; and this appears to be the result of the direct action of climate on the reproductive organs. In the best account which I have seen, it is stated that many of the varieties in the United States consist of three forms, namely, females, which produce a heavy crop of fruit; of hermaphrodites, which “seldom produce other than a very scanty crop of inferior and imperfect berries”; and of males, which produce none. The most skillful cultivators plant “seven rows of female plants, then one row of hermaphrodites, and so on throughout the field.” The males bear large, the hermaphrodites mid-sized, and the females small flowers. The latter plants produce few runners, while the two other forms produce many; consequently, as has been observed both in England and in the United States, the polleniferous forms increase rapidly and tend to supplant the females. We may therefore infer that much more vital force is expended in the production of ovules and fruit than in the production of pollen.
CAUSES OF STERILITY AMONG PLANTS.
If the sexual elements belonging to the same form are united, the union is an illegitimate one, and more or less sterile. With dimorphic species two illegitimate unions, and with trimorphic species twelve are possible. There is reason to believe that the sterility of these unions has not been specially acquired, but follows as an incidental result from the sexual elements of the two or three forms having been adapted to act on one another in a particular manner, so that any other kind of union is inefficient, like that between distinct species. Another and still more remarkable incidental result is that the seedlings from an illegitimate union are often dwarfed and more or less completely barren, like hybrids from the union of two widely distinct species.
AN “IDEAL TYPE” OR INEVITABLE MODIFICATION?
It is interesting to look at one of the magnificent exotic species (orchids), or, indeed, at one of our humblest forms, and observe how profoundly it has been modified, as compared with all ordinary flowers—with its great labellum, formed of one petal and two petaloid stamens; with its singular pollen-masses, hereafter to be referred to; with its column formed of seven cohering organs, of which three alone perform their proper function, namely, one anther and two generally confluent stigmas; with the third stigma modified into the rostellum and incapable of being fertilized; and with three of the anthers no longer functionally active, but serving either to protect the pollen of the fertile anther or to strengthen the column, or existing as mere rudiments, or entirely suppressed. What an amount of modification, cohesion, abortion, and change of function do we here see! Yet hidden in that column, with its surrounding petals and sepals, we know that there are fifteen groups of vessels, arranged three within three, in alternate order, which probably have been preserved to the present time from being developed at a very early period of growth, before the shape or existence of any part of the flower is of importance for the well-being of the plant.
Can we feel satisfied by saying that each orchid was created, exactly as we now see it, on a certain “ideal type”; that the omnipotent Creator, having fixed on one plan for the whole order, did not depart from this plan; that he, therefore, made the same organ to perform diverse functions—often of trifling importance compared with their proper function—converted other organs into mere purposeless rudiments, and arranged all as if they had to stand separate, and then made them cohere? Is it not a more simple and intelligible view that all the Orchideæ owe what they have in common to descent from some monocotyledonous plant, which, like so many other plants of the same class, possessed fifteen organs, arranged alternately, three within three, in five whorls; and that the now wonderfully changed structure of the flower is due to a long course of slow modification—each modification having been preserved which was useful to the plant, during the incessant changes to which the organic and inorganic world has been exposed?
SPECIAL ADAPTATIONS TO A CHANGING PURPOSE.
It has, I think, been shown that the Orchideæ exhibit an almost endless diversity of beautiful adaptations. When this or that part has been spoken of as adapted for some special purpose, it must not be supposed that it was originally always formed for this sole purpose. The regular course of events seems to be, that a part which originally served for one purpose becomes adapted by slow changes for widely different purposes. To give an instance: in all the Ophreæ, the long and nearly rigid caudicle manifestly serves for the application of the pollen-grains to the stigma, when the pollinia are transported by insects to another flower; and the anther opens widely in order that the pollinium should be easily withdrawn; but, in the Bee ophrys, the caudicle, by a slight increase in length and decrease in its thickness, and by the anther opening a little more widely, becomes specially adapted for the very different purpose of self-fertilization, through the combined aid of the weight of the pollen-mass and the vibration of the flower when moved by the wind. Every gradation between these two states is possible—of which we have a partial instance in O. aranifera.
