Phylum

“ The phyla or groups of forms are great trunks bearing many branches and twigs, but not giving rise to one another. Still less do the little side branches of one trunk bear the whole great trunk of another animal or plant phylum. But they all grow from the same roots among the primitive forms of life. ”

“ The animals belonging to this large and important collection, which compose the arthropod phylum, have certain common characteristic features. We find a body made up of a series of more or less completely similar segments placed one behind the other. ”

“ He who will carefully examine the flowers of orchids for himself will not deny the existence of the above series of gradations — from a mass of pollen-grains merely tied together by threads, with the stigma differing but little from that of an ordinary flower, to a highly complex pollinium, admirably adapted for transportal by insects; nor will he deny that all the gradations in the several species are admirably adapted in relation to the general structure of each flower for its fertilisation by different insects. ”

“ On the other hand, in these simple organisms there is no division into stem, leaves, and flowers, almost every portion is concerned in the process of reproduction—each filament or frond represents a perfect herb, shrub, or tree, and every sporiferous cell is the analogue of a flower. In the phænogamic class the floral colours are useful as attractions to insects of various kinds, which, visiting them for food, carry away the pollen to other flowers, and so conduce to their fertilization. ”

“ But before the examination of the Algae, and soon after of the Fungi also, led to such great results, the systematic botany of the higher plants underwent important changes through the methodical study of the embryology of the Muscineae and Vascular Cryptogams. These groups had been frequently and carefully examined by good observers since the last century, and the systematists, without penetrating deeply into the peculiarities of their organisation, had brought the species and genera, the families and even the higher divisions into tolerable order. ”

“ 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. ”

“ In consequence of this deficiency of the essential characters on which the determinations of the botanist are founded, there exists a necessity for examining more minutely and accurately than has yet been done, the internal structure of recent plants; their habits of growth, the cicatrices or scars left on the stem by the leaves that are spontaneously shed, the different appearances which their fruits exhibit in their various stages of development—all these points must be minutely studied before we can obtain any certainty as to the identity of fossil and living species of plants. ”

“ 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. ”

“ For instance, the aëthalium—to show the impossibility of a definite boundary—is sometimes observed as a flying vibrio, then a crawling amœba-like drop of sarcode; then, in the still condition, a greenish spherical cell like some protococus; even this mysterious creature need no longer be regarded as amphibious. In every stage it is decidedly exothentic.
What, then, is the distinction, and how does the evolution advance? Let us go back a little. We observe that in plants evolution advances by a folding down of the creature upon itself—an involution. ”

“ They afford the first positive proof as yet obtained of the co-existence of a varied fauna of the highest class of vertebrata with that ample development of reptile life which marks all the periods from the Trias to the Lower Cretaceous inclusive, and with a gymnospermous flora, or that state of the vegetable kingdom when cycads and conifers predominated over all kinds of plants, except the ferns, so far, at least, as our present imperfect knowledge of fossil botany entitles us to speak. ”

“ 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. ”

“ A few sea-weeds and zoophytes, or plants and animals of the simplest organization, were alone capable of existing in a state of things so unfixed and unstable. But in proportion as the conditions of existence improved, and great convulsions and catastrophes became rarer and more partial, flowering plants were added to the cryptogamic class, and by the introduction of more and more perfect species, a varied and complex flora was at last established. ”

“ The assumption to which we are committed by the hypothesis of evolution, that such so called unicellular plants were at first the only kinds of plants, is in harmony with the fact that habitats not occupied by plants of higher orders, commonly contain these protophytes in great abundance and great variety. The various species of Pleurococcaceæ, of Desmidiaceæ, and Diatomaceæ, supply examples of morphological units living and propagating separately, under numerous modifications of form and structure. ”

“ We read, for instance, at page 9, 'The appearance, as though the like was always repeating itself in nature, is suggested when we glance back from our station in time upon the succession of former epochs. Here we find the real first beginnings of species and genera, and even of orders and classes in the vegetable and animal kingdoms; we see at the same time that more or less thorough transformations are connected with the appearance of the higher grades in the organic kingdom, so that genera and species of the old world disappear, and new ones step into their place. ”

“ FOSSIL PLANTS AND PHYLOGENY.
Not only is it possible to derive valuable aid in the correlation of strata from the facts of plant distribution, but we may often follow the various stages in the history of a particular genus as we trace the records of its occurrence through the geologic series. In studying the march of plant life through past ages, the botanist may sometimes follow the progress of a genus from its first appearance, through the time of maximum development, to its decline or extinction. ”

“ And when we examine the record,—the forms of the leaves, the structure of the tissues, we get the same result as before, that the plants belonged to a flora which had no species in common with that which adorns the modern earth. Very gradually, and only after many successions, not of individual generations, but of the cycles of species, genera, and even families, did the vegetable creation conform itself to ours. ”

“ These curious organisms are among the most puzzling forms with which the botanist has to do, as they are so much like some of the lowest forms of animal life as to be scarcely distinguishable from them, and indeed they are sometimes regarded as animals rather than plants. At certain stages they consist of naked masses of protoplasm of very considerable size, not infrequently several centimetres in diameter. ”

“ The first idea which naturally occurred to me was, that this species was tending towards a dioecious condition; that the long-styled plants, with their longer pistils, rougher stigmas, and smaller pollen-grains, were more feminine in nature, and would produce more seed;—that the short-styled plants, with their shorter pistils, longer stamens and larger pollen-grains, were more masculine in nature. ”

“ Another reflection is equally strong in my mind—that the means which have been adduced to explain the origin of the species by 'natural selection,' or a process of variation from external influences, are inadequate to account for the phenomena. The law of phyllotaxis, which governs the evolution of leaves around the axis of a plant, is as nearly constant in its manifestation as any of the physical laws connected with the material world. ”

“ In his technical view the Angiosperm is distinguished by the structure of its reproductive apparatus, its flowers, and some recent botanists wonder whether the key to this expansion of the flowering plants may not be found in a development of the insect world and of its relation to vegetation. In point of fact, we have no geological indication of any great development of the insects until the Tertiary Era, when we shall find them deploying into a vast army and producing their highest types. ”

“ The facts of palæontological botany are opposed to Evolution, but they testify to Development, to progression from lower to higher types. The cellular Algæ preceded the Vascular Cryptogams and the Gymnosperms of the Newer Palæozoic rocks, and these were speedily followed by Monocotyledons, and, at a much later period, by Dicotyledons. ”

“ Darwin says: [2] "In a highly organized and complex animal, the gemmules thrown off from each different cell or unit throughout the body must be inconceivably numerous and minute. Each unit of each part, as it changes during development—and we know that some insects undergo at least twenty metamorphoses—must throw off its gemmules. All organic beings, moreover, include many dormant gemmules derived from their grandparents and more remote progenitors, but not from all their progenitors. ”

“ Accordingly, our first business is to describe rejuvenescence, multiplication, and distribution of individuals, and to show by what means a plant, considered as a separate organism, maintains itself, takes possession of its habitat and is enabled to keep its hold on that habitat, up to the moment when it is replaced by descendants endowed with a vitality of their own." The discussion of the Genesis of Plant Offspring relates to asexual reproduction by spores and thallidia, and by buds or roots, stems, and leaves ”

“ While the polyphyletic origin of species is in a fair way to be decided by experiment, it receives support from several well-known phenomena. The striking similarity in the plant body of families taxonomically so distinct as the Cactaceae, Stapeliaceae, and Euphorbiaceae, or Cyperaceae and Juncaceae, indicates that a vegetation form may be polyphyletic. ”

“ It was evident that such facts as these, as well as many others, could only be explained on the supposition that species gradually become modified; and the subject haunted me. But it was equally evident that neither the action of the surrounding conditions, nor the will of the organisms (especially in the case of plants) could account for the innumerable cases in which organisms of every kind are beautifully adapted to their habits of life—for instance, a woodpecker or a tree-frog to climb trees, or a seed for dispersal by hooks or plumes. ”

“ We do not aspire to a treatise on botany, but stop to consider only certain facts which are essential to this argument; a consideration of the higher plants will serve our purpose. Certain phytons are modified to become roots, which are the organs devoted to the absorption from the earth of the materials which are to be woven into the plant; other phytons become the stem for support; others the branches for expansion; others the leaves for respiration; others pistils and stamens for reproduction, while others become floral envelopes for their protection. ”

“ Nor ought we to feel much surprise at the affinities of cells and gemmules varying, when we remember the many curious cases given in the seventeenth chapter, of plants which absolutely refuse to be fertilised by their own pollen, though abundantly fertile with that of any other individual of the same species, and in some cases only with that of a distinct species. ”

“ Among plants utilization of the larger by the smaller—of trees by epiphytes and parasites—must have arisen since the times when the larger came into existence—times relatively late in the course of organic evolution. Moreover most of the plants which utilize others, either by climbing up them or settling themselves high up on their stems or sucking their juices, are phænogams, and the plants they utilize are also phænogams ”

“ And thus we might proceed through all the orchid genera, each new device, though based upon one of the foregoing plans, affording its new surprise in its special modification in adaptation to its insect sponsor—all these various shapes, folds of petals, positions, colors, the size, length, and thickness of nectary, the relative positions of pollen and stigma, embodying an expression of welcome to the insect with which its life is so marvellously linked. ”