Symbiosis

“ In some cases a relationship exists which is not parasitic but symbiotic. The term symbiosis, which is commonly used by biologists to define this relationship, means living together in mutual helpfulness. ”

“ It is not difficult to see, then, that natural selection will aid in the perpetuation of the symbiosis, and in cases 389 like that of the ginger-beer plant it is extremely difficult to get the two organisms apart, a difficulty similar to that in the case of the soredia of lichens. ”

“ Swimmerets: gill or plate-like structures in the aquatic larvae of some Neuroptera, serving as oars or organs of locomotion.
Swimming paddles: terminal appendages of mosquito pupae.
Swoked: smoky, suffused with gray or blackish.
Sylvan: species inhabiting forests or woodland areas.
Symbiogenesis: the method of origin of social symbiotic relation among ants and other insects.
Symbiosis: a life relationship existing between different kinds of animals or plants, or between animals and plants: true symbiosis is where both parties to the relation benefit: see also parasitism, commensalism. ”

“ And as color is developed little by little as the result of insect-vision, modifications of structure are developed, in equal pace, by insect-touch. [3]
This is not all. An organism is modified by all which environs it. Mr. Spencer, in his great work on "Biology," has shown us that the form of the cell, the leaf, the branch, the trunk, the flower, is determined in great part by the environment. Varying amounts of sunshine or shade modify the form of a branch. A prevailing wind modifies the form of a tree. A change of position on the stem changes the form of a flower. ”

“ As to somatogenetic factors—granting that structural changes in the body (body-cells) of an animal or plant can profoundly influence in some way the germ-cells, and that, therefore, acquired characters can be transmitted—they are many and well defined. Some of them are the habitat of an animal or plant, the temperature, climate, air, food, soil, water, structures in use or disuse (so-called “Use” and “Disuse”) , etc.
The following brief descriptions will enable the reader to understand that change in the surroundings (environment) of a living creature may cause its body (body-cells) to vary. ”

“ Such a speck of living protoplasm as the amoeba is known to biologists as a cell; and of such cells or variations of them the structures of all plants and animals are built up, a plant or animal composed of a single cell being known as a unicellular organism, whereas a plant or animal composed of a plurality of associated cells is known as a multicellular organism. Since such unicellular organisms as the amœba are fairly observable, we may conveniently begin the study of life at that stage of evolution which they have reached. ”

“ We must be content to follow the evolution of the higher types of organisms. I will therefore first describe the advance of the Tertiary vegetation, the luxuriance of which was the first condition of the great expansion of animal life; then we will glance at the grand army of the insects which followed the development of the flowers, and at the accompanying expansion and ramification of the birds. The long and interesting story of the mammals must be told in a separate chapter, and a further chapter must be devoted to the appearance of the human species. ”

“ Next let us touch upon the plan which connects the plant with the animal world. The wonderful adaptations of many flowers and insects to each other, as to the fertilization of the former, and as to the life of the individual insect and the propagation of its kind, are evidence of design. For example, there are certain species of plants that are dependent for their fertilization on certain species of moths which live in the flowers, and the moths, in turn, are dependent on the plants. They deposit their eggs in the ovaries of the flowers where the young are hatched and nourished. ”

“ Besides the vital action observable in the growth and development of plants, we know, of course, that plants sicken and die, and manifest all other attributes of living forms. There is no room for argument about the presence of life in the plant kingdom.
But there are other forms of life far below the scale of the plants. There is the world of the bacteria, microbes, infusoria—the groups of cells with a common life—the single cell creatures, down to the Monera, the creatures lower than the single cells—the Things of the slime of the ocean bed. ”

“ It has already been indicated that ecology bears the closest of relations to morphology and histology on the one side, and to physiology on the other—that it is, indeed, nothing but a rational field physiology, which regards form and function as inseparable phenomena. The closeness with which it touches plant pathology follows directly from this, as pathology is nothing more than abnormal form and functioning. Experimental work in ecology is purely a study of evolution, and the facts of the latter are the materials with which taxonomy deals. ”

“ A continuity of response having been established between the responses of inorganic matter on the one hand and living plants on the other, inquiry was continued to find out whether the fundamental physiological mechanisms were similar in plant and in animal life. The plant world affords an unique opportunity for studying the changes by which a simple and primitive organ becomes gradually transformed into one of greater complexity. ”

“ Passing from the evidence that evolution has taken place, to the question—How has it taken place? we find in known agencies and known processes, adequate causes of its phenomena.
In astronomic, geologic, and meteorologic changes, ever in progress, ever combining in new and more involved ways, we have a set of inorganic factors to which all organisms are exposed; and in the varying and complicating actions of organisms on one another, we have a set of organic factors that alter with increasing rapidity. ”

“ In all this the moving creating life of the original fluid cannot pass unnoticed, and becomes still more evident if we examine the history of the origin of organized bodies, in which the fluid appears as the basis both of animal and vegetable life; and thus the very germ of individual organisms is intimately connected with the life of the planet. Indeed this is partly true of the solid parts of the earth; for it is easy to show, even in the fossil kingdom, a transition partly to animal and partly to vegetable life ”

“ It is that this universal trait of the Metazoa and Metaphyta, must be ascribed to the primitive action and re-action between the organism and its medium. The operation of those forces which produced the primary differentiation of outer from inner in early minute masses of protoplasm, pre-determined this universal cell-structure of all embryos, plant and animal, and the consequent cell-composition of adult forms arising from them. ”

“ The spectacle afforded by the wonderful energies imprisoned within the compass of the microscopic cell of a plant, which we commonly regard as a merely passive organism, is not easily forgotten by one who has watched its movement hour by hour without pause or sign of weakening. The possible complexity of many other organisms seemingly as simple as the protoplasm of the plant just mentioned dawns upon one, and the comparison of such activity to that of higher animals loses much of its startling character. ”

“ Given, then, that pressure which species exercise on one another, in consequence of the universal overfilling of their respective habitats—given the resulting tendency to thrust themselves into one another's areas, and media, and modes of life, along such lines of least resistance as from time to time are found—given besides the changes in modes of life, hence arising, those other changes which physical alterations of habitats necessitate—given the structural modifications directly or indirectly produced in organisms by modified conditions ”

“ These changes, which would go to but a comparatively small extent were organisms exposed to constant external conditions, are kept up by the continual changes in external conditions, produced by astronomic, geologic, meteorologic, and organic agencies: the average result being, that on previous complications wrought by previous incident forces, new complications are continually superposed by new incident forces. And hence simultaneously arises increasing heterogeneity in the structures of individuals, in the structures of species, and in the structures of the Earth's Flora and Fauna. ”

“ Thus we have an unbroken series—certain substances condensing out of cosmic vapour, some of them combining to form the variety of rocks, soils, metals, &c., and others giving rise to protoplasm which grows' and develops into a thousand shapes and hues, of insect, fish, reptile, bird, and beast. ”

“ Consequence the first.—If the plant, exposed alike to gravitation and light, is divided into root and stem, into a terrestrial and an atmospheric part, the animal, being more independent, is less bound to the organism of the planet to which it originally belongs, and is consequently more under the influence of light; wherefore, though sometimes fettered to the earth, it is by no means fixed or rooted in it, to which circumstance it owes its faculty of locomotion. ”

“ Increasing Complexity of Structure and of Habits in Plants and Animals.—In our study of biology so far we have attempted to get some notion of the various factors which act upon living things. We have seen how plants and animals interact upon each other. We have learned something about the various physiological processes of plants and animals, and have found them to be in many respects identical. We have found grades of complexity in plants from the one-celled plant, bacterium or pleurococcus, to the complicated flowering plants of considerable size and with many organs. ”

“ In this connection we must keep in view the fact that every visible character in a plant is the resultant of the cooperation of specific structure, with its various potentialities, and the influence of the environment. We know, that in a pure species all characters vary, that a blue-flowering Campanula or a red Sempervivum can be converted by experiment into white-flowering forms, that a transformation of stamens into petals may be caused by fungi or by the influence of changed conditions of nutrition, or that plants in dry and poor soil become dwarfed. ”

“ The first organic forms of the protoplasm, the first aggregations of cells, the protozoons, the zoophytes or plant-animals, the gelatinous mussels of the still warm seas, were succeeded by the fishes, then by the reptiles, the birds, the mammals, and lastly man, who at present occupies the top of the genealogical tree, and crowns the animal kingdom. ”

“ Finally, the power of propagation possessed by each separate cell, using the term in its largest sense, determines the reproduction, the variability, the development and renovation of each living organism. No other attempt, as far as I am aware, has been made, imperfect as this confessedly is, to connect under one point of view these several grand classes of facts. We cannot fathom the marvellous complexity of an organic being; but on the hypothesis here advanced this complexity is much increased. ”

“ Now when surface-tension (for instance) causes a minute semi-fluid organism to assume a spherical form, or gives the form of a catenary or an elastic curve to a film of protoplasm in contact with some solid skeletal rod, or when it acts in various other ways which are productive of definite contours, this is a process of conformation that, both in appearance and reality, is very different from the process by which an ordinary plant or animal grows into its specific form. ”

“ Ah, why has not protoplasm, evolving by its own energy from one being into another, reserved until it came to us a little of that wonderful power which it has bestowed so lavishly upon the insects! The answer is that apparently, in this world, cellular evolution is not everything. ”

“ Where there is vegetation there are animals, not quadrupeds or bipeds necessarily, but numbers of small, it may be invisible, creatures which exist upon the vegetable kingdom—the algæ and minute creations of globules and cells, the infusoria already mentioned, the corals, etc. And in the “protozoa,” or first specimens of animal life, we have a similarity to the vegetable kingdom; we then get by gradual steps to other more perfect beings, each after his kind, till we arrive at the most perfect animal—Man. ”

“ These different elements must be held together by forces of attraction, and the direction of these forces must have some common centre represented by some differentiation of the protoplasm, whether as clearer spot, or as nucleus. This spontaneously generated organism, neither animal nor plant, is nourished, as we have seen, by diffusion, by the transformation of inorganic into organic substance. The lowest organisms possess no definite organs for taking food ”

“ In these tiny Protozoa, those organisms which consist of one single cell only, the Amœbæ, as well as those consisting of several cells in a state of union, the Synamœbæ, are able to perform all the functions of animal life—cohesion, sensation, motion, digestion, and reproduction; but, as the organism becomes more and more complex, these different functions are shared among several groups of cells. ”

“ The cells are living organisms springing from vital units, and can no more manifest themselves independently of these units than life can manifest itself independently of an actual organism. And they make their appearance in the proper environing conditions, just as the oak comes from its primordial germ or vital unit in the chemically changed conditions of the soil. Everywhere the vital germ or unit precedes the vital growth as the plant or tree precedes the natural seeds it bears. ”