Plant hybrid

“ It may here be mentioned, that whenever hybrids are to be raised, by fertilizing one plant with the pollen of another, the anthers of the flower that is to produce the seed, should be removed with a pair of scissors, before they burst. The pollen from the other flower which is to form the hybrid, should be afterwards applied with a camel-hair pencil to the stigma of the flower, which is to produce the seed; and a bit of thread should be tied round the flower-stalk, in order that the seed-pod may be saved, and set apart. All hybrids may be made in the same manner ”

“ At right is a segregate of the second hybrid generation exactly like its parent in size of plant, leaf and flower and in habit of growth.
for constant intermediate hybrid races which I think has never before been mentioned. In crossing species of the genus Nicotiana, I have had plants develop from seed that have apparently been formed apogamously, that is, formed from an immature egg cell without fertilization. It is evident that this is induced by the extraordinary irritation of foreign pollen. The true hybrid plants that are formed are generally blends in the first generation. ”

“ Hybrid Perpetuals must be given special treatment in order to secure flowers from them throughout the season. Their blossoms are always produced on new growth, therefore, if [Pg 144] you would keep them producing flowers, you must keep them growing. This is done by feeding the plant liberally, and cutting back the branches upon which flowers have been produced to a strong bud from which a new branch can be developed. ”

“ Secondly, these hybrids are remarkable from differing much from one another in many of their characters; for hybrids of the first generation, if raised from uncultivated plants, are generally uniform in character. That these hybrids belonged to the first generation we may safely conclude, from the absolute sterility of all those observed by me in a state of nature and of the one plant in my garden, excepting when artificially and repeatedly fertilised with pure pollen, and then the number of seeds produced was extremely small. ”

“ Equally efficient in the hands of the cultivator has been another method of producing new forms—namely, hybridization. If the pollen of a plant be transferred to the stigma of a related species, offspring is often produced; and the product is a batch of plants intermediate in characters between the two parents, and generally uniform in appearance. ”

“ From this time the possibility of the existence of hybrid plants was admitted, and Linnæus, with many subsequent authors, published observations tending to show that, even in the natural state, new species were formed by two different plants, the pistil of one having been fecundated by the stamens of the other. This impregnation has been artificially applied, by modern cultivators, to the production of new varieties of fruits and flowers. ”

“ We may feel sure that plants have been rendered heterostyled to ensure cross- fertilisation, for we now know that a cross between the distinct individuals of the same species is highly important for the vigour and fertility of the offspring. The same end is gained by dichogamy or the maturation of the reproductive elements of the same flower at different periods,—by dioeciousness—self-sterility—the prepotency of pollen from another individual over a plant’s own pollen,—and lastly, by the structure of the flower in relation to the visits of insects. ”

“ Many varieties can be propagated securely by buds, but generally or invariably revert to their parent-forms by seed. So, also, hybridised plants can be multiplied to any extent by buds, but are continually liable to reversion by seed,—that is, to the loss of their hybrid or intermediate character. I can offer no satisfactory explanation of these facts. Plants with variegated leaves, phloxes with striped flowers, barberries with seedless fruit, can all be securely propagated by buds taken from the stem or branches ”

“ The balance of the reddish-purple plants, which comprise about two-thirds of the second generation, will, if their seeds are germinated, produce colored as against white-flowered progeny in the three-to-one ratio. In other words, these artificial crosses, made by the plant breeder, and this splitting up of hybrids which has been many times verified, are seen to be very fertile causes of the origin of new forms of plant life, if only the factor and character differences in the ancestry be sufficiently complex. ”

“ Now nature has settled that the right way to propagate plants is by means of seedlings. Strictly speaking, indeed, it is the only way; the other modes of growth from bulbs or cuttings are not really propagation, but mere reduplication by splitting, as when you chop a worm in two, and a couple of worms wriggle off contentedly forthwith in either direction. Just so when you divide a plant by cuttings, suckers, slips, or runners: the two apparent plants thus produced are in the last resort only separate parts of the same individual—one and indivisible, like the French Republic. ”

“ We will come to that some day in the future, maybe—not in our lifetime, but we will have hybrid varieties, because, after all, our great improvements that have come in most of our plants, in corn and in wheat, and in other plants, have come through the mixing of the genes, or the characters that we have differing between species. ”

“ There would be great range in variation of type from hybridization between oak trees and I have seen a number of oak trees that were evidently hybrids, where the parentage could be traced on both sides, that were held at very high prices by the nurserymen. I asked one nurseryman, who wanted an enormous price for one hybrid oak, why he didn't make ten thousand of those for himself next year? ”

“ In general, the success attending the production and perpetuity of hybrids among plants depends, as in the animal kingdom, on the degree of proximity between the species intermarried. If their organization be very remote, impregnation never takes place; if somewhat less distant, seeds are formed, but always imperfect and sterile. The next degree of relationship yields hybrid seedlings, but these are barren; and it is only when the parent species are very nearly allied that the hybrid race may be perpetuated for several generations. ”

“ God gives the seed a body "as it hath pleased Him, and to every seed its own body."
It is true that what are called "varieties" can be produced among cultivated plants, as among birds and animals, by change of food and climate, and by care and training. The same plant will soon look very different if taken from a dry, sunny spot, and placed in a damp, shady corner. I have heard that if plants are moved from their home on the seashore, and placed in a dry, hot place, their thick, fleshy leaves will in time quite change their character, becoming thin and hairy. ”

“ Hybrids are sometimes less fertile than pure-bred species, and are occasionally quite sterile. Some hybrids, however, are as fertile as pure-bred plants. Hybrid plants may be again crossed, or even re-hybridized, so as to produce a progeny of very mixed parentage. This is the case with many of our roses, dahlias, begonias, pelargoniums, orchids and other long or widely cultivated garden plants. ”

“ Indeed, the faculty of spontaneous reproduction and perpetuation necessarily supposes a greater power of accommodation, within a certain range, than we find in most domesticated plants, for it would rarely happen that the seed of a wild plant would fall into ground as nearly similar, in composition and condition, to that where its parent grew, as the soils of different fields artificially prepared for growing a particular vegetable are to each other. ”

“ Seeing that hybrid plants, which from their nature are more or less sterile, thus tend to produce double flowers; that they have the parts including the seed, that is the fruit, perfectly developed, even when containing no seed; that they sometimes yield gigantic roots ”

“ Critical field observations of plants in the wild state, supplemented by the cultivation side by side of species supposed to be distinct and by the lessons learned from experimental plant breeding, have developed the theory that many species, perhaps all, are composed of a greater or lesser number of races, differing from each other too little to cause them to be regarded as species, notwithstanding the fact that they may breed true from seed to such slight or trivial differentiations. ”

“ Such segregation into purples and whites may not he desirable; all purples may be wanted. This brings us to a consideration of class B of the four classes of phenomena attending hybridization, the production of desirable character combinations in the first hybrid generation and their continuation by asexual propagation. This class really includes several distinct types of occurrences. The purple sweet pea produced from the two whites will serve as an illustration of the first type. In certain plants (not meaning the sweet pea, however) it is as simple to reproduce by cuttings as by seed. ”

“ Towards the end of the month you can divide those herbaceous plants that are not spring-flowering, if you wish to increase them. You must not disturb plants that are just going to flower, but all the strong kinds will stand division and transplanting when they have only sent up young leaves. For instance, you could take up a Phlox, a Michaelmas Daisy, or even a Pyrethrum, on a showery day, pull it to pieces, and find that every bit made a strong plant by the autumn. In the rock garden the mossy Saxifrages that have bald places in the middle should be taken up, divided, and firmly replanted. ”

“ Artificial pollination of the female flowers of the local forms with pollen taken from American kinds has not yet succeeded in producing a permanent hybrid, although the result in the first generation has frequently shown great promise. ”

“ The plants which have varied by buds belong to so many orders that we may infer that almost every plant would be liable to variation, if placed under the proper exciting conditions. These conditions, as far as we can judge, mainly depend on long-continued and high cultivation; for almost all the plants in the foregoing list are perennials, and have been largely propagated in many soils, under different climates, by cuttings, offsets, bulbs, tubers, and especially by budding or grafting. ”

“ Hybrids are seldom raised by experimentalists in great numbers; and as the parent-species, or other allied hybrids, generally grow in the same garden, the visits of insects must be carefully prevented during the flowering season: hence hybrids will generally be fertilised during each generation by their own individual pollen ”

“ But seedlings have actually been produced in every case which I have named. It is one of the fixed rules in biology that the offspring of different species must be barren—otherwise the parents are not truly species—and that different genera will not breed at all. But in most instances which have been brought to the test as yet, hybrid orchids of different species prove fertile, and some bigeneric crosses yield a progeny at least. ”

“ But it has been found [39] that the hybrid may be fertilized by pollen taken from one of its parents, and that then the offspring assumes the characters of that parent. [10]
Natural hybrids do not often occur, though in diœcious plants, this seems to have been the case with willows that present such an intricate puzzle to botanists in their classification, so that it has become almost impossible to say what are the limits and bounds of some of the species. ”

“ All the flowers produced by the same plant have been developed from the same seed; those which expand at the same time have been exposed to exactly the same climatic influences; and the stems have all been nourished by the same roots. Therefore in accordance with the conclusion just referred to, no good ought to result from crossing flowers on the same plant. ”

“ On the other hand there is a larger group of cases of reversion by buds, which is probably not of hybrid nature, nor due to innate inconstancy of the variety, but must be considered as pure atavism. I refer to the bud-variations of so many of our cultivated varieties of shrubs and trees. Many of them are cultivated because of their foliage. They are propagated by grafting, and in most cases it is probable that all the numerous specimens [179] of the same variety have been derived in this way from one primitive, aberrant individual. ”

“ The hybrid offspring will therefore, in the main, have the character of the species and be indistinguishable from it, or show only such differences as escape ordinary observation. When occurring in the seeds of the variety they betray themselves as soon as the differential characters are displayed. Between the thousands of flowering plants of a white variety the hybrids will instantly catch the eye by their red or blue corollas. Quite the contrary effect results from the admixture of hybrids with the seeds of the species itself. ”

“ It does not matter how the variation is produced, so long as it is once allowed to occur. The variation in the plant once fairly started tends to become hereditary and reproduce itself; the seeds would spread themselves in the same way and take part in the struggle with the forty-nine hundred, or forty-nine thousand, with which they might be exposed. Thus, by degrees, this variety, with some slight organic change or modification, must spread itself over the whole surface of the habitable globe, and extirpate or replace the other kinds. ”