George Bentham

“ It has, therefore, been proposed entirely to reject descent as an element in the definition of species, and to consider as such any set of individuals which present, either in their external form, or in their internal structure, or in their biological phenomena, any common character, or combination of characters, distinguishing them from all others. ”

“ But the opinions I have on that and other occasions expressed, that genera, as such, have no independent existence in nature, have been in some measure misunderstood. Far be it from me to deny that groups of species exist in nature, resembling each other more than they do the species of any other group—that some of these groups, consisting of two, three, or any number of species, are in nature distinguished from all others by a number of well-marked characters, or that a single species may be so isolated ”

“ The truly German idea of taking one species or genus as a normal type of a genus or order, and grouping others around it as more perfect, or reduced, or collaterally aberrant forms, leads to no practical results. However well it may read in chamber speculations, it produces nothing but confusion when applied to the actual grouping of species. There is no plant which arguments like those usually brought forward may not show equally well to be an aberrant form of almost any number of different types. ”

“ The cultivation must be that of the gardener, whose object is to raise new varieties—not of the curator, desirous of keeping his botanic garden usefully cropped, and correctly named—still less of the botanist, who seeks to uphold a species he has set up. The former sows extensively in different localities, in order to have the greater chance of accidental aberration; he carefully watches his seedlings as they grow up, and selects his seeds for the next generation from such plants as show the slightest tendency to vary in the wished-for direction. ”

“ The most important character, in plants, will always be that which in the greatest number of species (or groups of species) is the most constantly accompanied by the greatest general resemblances among those species, and differences from all others—that which collects into the same group species showing the greatest general conformity in the structure and economy of all their parts, and which may, therefore, be supposed to be the most uniformly influenced by or acting upon the specific constitution of plants. ”

“ The specific identity of two or more individuals admits, therefore, but very rarely of positive proof; we must judge of it by inductive evidence, selecting by the careful consideration of what characters are known, especially in allied species, to remain permanent generation after generation, unaltered by change of soil, climate, or other circumstances, and what are the variations occasioned by causes which we can appreciate, or which are known to occur without assignable cause. ”

“ The Species, in the ordinary traditional acceptation of the word, designates the whole of the individuals supposed to be descended from one original plant, or pair of plants. But this definition is practically useless—for we have no means of ascertaining the hereditary history of individual plants—and is considered theoretically incorrect by those who deny the original creation of a certain number of individuals, or pairs of individuals, forming each a parent stock, from which as many constantly distinct races have descended. ”

“ With regard to direct experiment in aid of inductive reasoning, it has been said that cultivation is a sure and easy test of the identity or distinctness of species; and nothing is more common than to find as an argument in support of a "critical" species, that it has been growing for many years in a garden, always retaining its distinctive characters. ”

“ But in plants we are much less able even than in animals to trace the modifications of form and structure to any final causes. The animal goes after, and selects his food; and the whole economy of his structure is modified according to the nature of that food, and where and how it is to be obtained. ”

“ Admitting, however, that in the extensive and diversified Flora of Europe, wild hybrids have been observed in some twenty to twenty- five genera, if we consider that the species in those genera which will hybridise are but few; that the individuals raised are always very few, and often isolated; that they are either not reproduced in a second generation, or their offspring is a further approach to the parent species; and that even two individuals sprung directly from the same two parent species generally differ quite as much from each other as from one of their parents ”

“ The plant is stationary and must take what food comes within its reach; and that food, and the mode of absorbing it, is very similar in all species; nor can we discover any other final cause why one set of plants, for instance, should always have alternate and another opposite leaves—why in Digitalis purpurea there should be on an average 1200 seeds fecundated and ripened for every two pair of stamens, whilst in several Acacias there should be 10,000 stamens to every head of flowers, which sets and ripens some half-dozen or a dozen seeds only. ”

“ The existence of hybrids in the vegetable kingdom, less perfect in their nature than true species, analogous to the mule among animals, has at all times been a popular notion; and wild plants, having some resemblance to cultivated or useful ones, but less perfect in respect of the qualities sought from them, have in most countries been stigmatised as bastards. ”

“ It is true that, exceptionally, embryos may be formed and brought to perfection without normal fertilisation, but so also the whole series may be dispensed with, and plants are reproduced by buds without passing through the embryo state; but in all phanerogamic species, for their normal reproduction, the whole series, the male organs, the female organs, and the organs of maturation, are equally essential. ”

“ The blind adherence to a pre-established scale, in distributing into genera the species of a large order, renders such a classification purely artificial. It had been ascertained that the relative arrangement of the radicle and cotyledons in the embryo of Cruciferæ, the relative prominence of the ribs of the fruit, and the number and arrangement of the vittas in Umbelliferæ, the various modifications of the pappus in Compositæ, were in many cases remarkably constant, not only in species, but in many very natural genera. ”

“ Others, on the contrary, of our most acute observers, having acquired convincing evidence of natural hybridity in a few cases, have generalized their conclusions; they have supposed natural hybrids to be of constant and frequent occurrence; and they have ascribed to this cause alone the majority of variations from the supposed typical forms of species, or even attributed to original hybridisations the multitude of nearly allied, but constant species, in several of the largest genera. ”

“ Not only are the specimens preserved generally unaccompanied by any notes on the comparative frequency of the form gathered, and others closely resembling it, or on any other local circumstances affecting the question, but they are very likely to lead the botanist astray in these particulars. A collector is naturally struck by a plant differing in aspect from the generality of its species, and gathers it in preference to the forms more familiar to him. ”

“ It has happened to most close observers to have on some occasion brought forward some character till then comparatively neglected, but which has proved to be eminently useful for establishing natural groups in particular genera, orders, or classes. Such a character is then apt to assume an undue importance in the observer's mind, and to be applied by him indiscriminately throughout the vegetable kingdom. ”

“ It is where the species is most at home, where it accommodates itself most readily to a variety of soils and exposures, where the stations it affects show a most ancient domicile, that the connecting links between the varieties it has produced must generally be sought for. And this is one great reason why permanence of form is so little conclusive as evidence of specific difference, unless observed in a considerable portion of the area of the species. ”

“ A purely natural method of arranging species and genera is impossible; at least, none has ever been brought forward. The affinities and cross-affinities of plants are so complicated and intertwined, that we have no method of representing them either by a linear series, or by mapping them out on a plane surface. Many of the most natural groups have no definite limits ”

“ This temporary character, when wild, may be observed in all the extraordinary aberrations from the common form, however healthy the individuals may appear, such as Orchis pyramidalis with spurless flowers, or Linaria vulgaris, with five spurs; Helianthemum vulgare, or Narcissus juncifolius, with linear or divided petals; or Stellaria Holostea, with no petals at all, &c.; they are none of them perpetuated; they cannot resist the immense chances there always are against the offspring of any one individual plant ever coming to perfection. ”

“ In other species, cross-breeding between individuals or races is rare and exceptional, and apt to be unfruitful. [2]
Plants of distinct species breed together only under exceptional circumstances.
The hybrids thus produced are constitutionally more or less imperfect. They seldom produce a second generation, unless fertilized by an individual of one of the parent species, to which they then gradually return. They, therefore, do not establish permanent races, but disappear in nature, unless reproduced by a fresh cross-breeding between the parent species. ”

“ And yet characters like these are, in some instances, so constantly accompanied by so many general resemblances as clearly to distinguish natural groups of several thousand species.
The importance of organs, also, in another way, admits of two distinct qualifications, not always concurrent: physiological importance and systematic importance. ”

“ The object is not to show how long a particular form can be made to endure, but that it will always endure, in spite of external influences or other accidents—that it will not vary under any circumstances, or at any time. ”

“ So in the genus Dianthus, according to C. P. Gaertner, artificial hybrids are very readily produced, and are more fertile than those of almost any other plants, and yet wild hybrids are very rare. Lecoq, it is true, speaks of hybrids between D. Monspessulasnus and D. Seguieri as being very abundant in the Montdore, and certainly these two species are, in that locality, very variable, but not more so than I have observed them in the Pyrenees, Provence, &c., when growing separately. ”

“ Upon the whole, as far as my own experience goes, the results of cultivation constitute an item, but one item only, and that often a fallacious one, among the evidences on which the permanency of character is to be judged by inductive reasoning.
Even the proof of specific identity by cultivation is often liable to error. Such experiments are often several years in carrying on ”

“ The preparation of large collections for distribution has given me opportunities of studying many American, African, and Asiatic species in large masses of specimens. In some of the more important monographs I have worked up, I have been enabled to compare the materials of the principal herbaria of Europe; and, since my working-stock has been transferred to Kew, the daily consultation of such a collection as that of Sir William Hooker has contributed very much to confirm my ideas as to the variability and limitation of species ”

“ Seeds of a plethoric kitchen-garden vegetable, originally the result of a peculiar treatment in a rich soil, will, even under a different and uncongenial treatment, to a certain degree reproduce the same variety for some generations. ”

“ But by taking these characters as absolute, and considering every slight modification of them as of generic importance, many of the most natural groups in those orders have been broken up, and split down almost to single species, classed into purely artificial tribes and sub-tribes. So, also, a character generally important may, in some instances, separate a single species from a large order with which it may agree in every other respect. ”