Plant breeder

“ If species and varieties can be distinguished only by factor differences, as the plant breeders no doubt correctly insist, it becomes obvious enough that we have in cross-fertilization to consider not alone the factor differences of the pistillate or female, but also of the staminate or male contribution to the union, and how these are reflected in the progeny. Our knowledge of this has practically all been based on work done on cultivated plants under control conditions and it shows some interesting developments which occur from crossing. ”

“ It is interesting at this point to recall one of the most common differences between plant and animal breeding which is seldom clearly recognized by practical breeders. Plant breeders most commonly strive to produce new races or breeds with distinctive characters which will reproduce their desirable qualities without continuous selection; while animal breeders almost wholly limit their attention to selection within the breeds already established, to maintain them in the highest state of efficiency possible. ”

“ In other cases it is only possible to pick out the individual plants which breed true by growing their seed and observing how it behaves. If it produces progeny all of which are like the plant from which the seed was obtained, that plant is a fixed type and will breed true continuously in the future. The final result of the experiment was to obtain in three years from the time the cross was made, four fixed types which subsequent experience has shown breed true continuously, a long eared bearded type, a short eared beardless type, a long eared beardless type and a short eared bearded type. ”

“ After commenting on these purely imaginary causes, I pointed out in 1832, as the two great flaws in Lamarck's attempt to explain the origin of species, first, that he had failed to adduce a single instance of the initiation of a new organ in any species of animal or plant; and secondly, that variation, whether taking place in the course of nature or assisted artificially by the breeder and horticulturist, had never yet gone so far as to produce two races sufficiently remote from each other in physiological constitution as to be sterile when intermarried, or, if fertile, only capable of producing sterile hybrids, &c. ”

“ We have within a decade discovered the laws of plant breeding. We know a good deal more about it now than ever before and are in a position to start about it very deliberately and with a reasonable certainty that we are going to get certain combinations of qualities if we keep at it long enough. ”

“ More seed will then be produced, and the seedlings being the product of cross-fertilisation will be vigorous, so that the species will tend to increase in number, to be again checked, as soon as the plant again grows in crowded masses. ”

“ But suppose we are dealing with red clover where the flowers are small, almost sterile with their own pollen and produce only one seed. In this crop, the long and tedious method of continuous selection just mentioned must be used, for there is no other way. This method is often called the pedigree-culture method. The main idea of the plan is that the seeds of single plants are grown in isolated plots, and the character of the mother plant judged by the characters of the progeny. ”

“ In the flower where the father and mother part matures at the same time, self-fertilization is the rule. Cross-fertilization occurs in instances where either the father part or mother part ripen at different times, in these cases the pollen is carried from plant to plant by the wind or by the nectar-seeking bees. ”

“ There must, as in the wind-carried pollen, be a tremendous wastage, yet sufficient quantities of it do fertilize the females, particularly in the ditch grass, which fruits very freely.
Whether it be any of the various contrivances for insect fertilization, or by the winds, or, as in the eelgrass, by the water, the climax of the flower’s life is always reached in this act. For all annuals the plants, also, begin to die down then, a process that is completed with the production of seed, which is, of course, the object of all those varied modes of fertilization. ”

“ In this way the nectar-seeking insects would often carry pollen from the flower of one plant to the stigma of another plant’s flower, and thus secure cross-fertilization. Undoubtedly often the stigma of a plant’s flower was fertilized by pollen from the same flower; but it is known that seeds produced by cross-fertilization are much more vigorous and hardy than those produced by self-fertilization in the same flower; therefore, those plants that varied most in the direction best adapted for securing cross-fertilization would have decided advantages in the struggle for existence. ”

“ If, on flying away, he next visits another male blossom on the same plant, he only collects still more pollen. But if he happens to flit off to a female flower, he brushes off some of the pollen, as he passes, on to the feathery, sensitive surface protruded by the plant right in his path, on purpose to meet him. In this way, each female blossom makes perfectly certain of due fertilization from a separate organism; and such cross-fertilization, as Darwin has shown, produces in the long run the most fertile seeds, and the strongest, heartiest, and most vigorous seedlings. ”

“ Having first been nomads, domesticators and breeders of animals; they eventually became husbandmen, breeders of trees and plants, and they undoubtedly found that the principles which were so usefully employed in producing animal variations could also be used in producing and fixing plant varieties. The pollen or germ of an outstanding good male individual, when brought into contact with the pistil or ovum of an outstanding female individual of the same species will produce a scion that is more likely than any other to have good qualities. ”

“ When a gardener wishes to obtain variations of a plant from which to select and establish a new breed, he deliberately sets to work to disturb—to shake up, to act upon in a tentative, experimental way—the germ-plasm of one or more parent plants by change of soil, climate, food and often by cross-fertilizing them with another breed or variety. ”

“ In Table 7/C the crossed plants are the offspring of a cross with a fresh stock, or with a distinct variety; and they were put into competition either with self-fertilised plants, or with intercrossed plants of the same old stock. By the term fresh stock I mean a non-related plant, the progenitors of which have been raised during some generations in another garden, and have consequently been exposed to somewhat different conditions. ”

“ The science of plant breeding, too long neglected by the countrymen of Darwin, has been pursued with much success for a decade, and has already reached the "producing stage" in respect of new and improved races of agricultural plants. ”

“ And if careful research and experiment do not result in absolute certainty, they will yet render the production of fine varieties of fruit, by the crossing of the old ones, a matter of much less chance than it now is.
The art of cross-fertilization is being much more practised by florists than by pomologists, and for obvious reasons. What the breeder of annuals can do in a few months requires more than as many years from him that essays to raise new fruits. ”

“ We now come to a far more general and therefore more important means by which the mutual fertilisation of distinct plants is effected, namely, the fertilising power of pollen from another variety or individual being greater than that of a plant’s own pollen. ”

“ Although the plants raised during ten successive generations from crosses between distinct yet inter-related plants almost invariably exceeded in height, constitutional vigour, and fertility their self-fertilised opponents, it has been proved that seedlings raised by intercrossing flowers on the same plant are by no means superior, on the contrary are somewhat inferior in height and weight, to seedlings raised from flowers fertilised with their own pollen. ”

“ This is very suggestive of the way by which through a selection of parents we have changed the cow so marvelously for milk production. The object of selection here is to find desirable strains that produce uniform progenies. Page 15 shows that tree breeding has a more easily attainable objective—namely, one good specimen.
Second, varying combinations in offspring of qualities of parents. A hybridization of hazels and filberts (Fig. 20) produced plants ranging from 12 inches to 12 feet in height—suggestive of variations in great degree for each quality a plant can have. ”

“ The rapid development of the science and art of breeding places us to-day in position to secure improvements much more rapidly than has been done in the past. It would not be astonishing if from 25 to 50 years of careful, intelligent breeding would accomplish with a wild plant what has required many centuries under the crude methods of our ancestors.
It may be asked why we should be in haste to take up the improvement of our native plants. ”

“ By fertilizing white flowers with pollen from red ones we can almost always get seeds that will develop into plants bearing flowers that are not white. What is true of color is true of other characteristics of the plant, such, for instance, as size and shape of leaves, habit of growth, size, shape, and quality of fruit, etc. Thus by careful cross-fertilization, we are able to produce not only beautiful and new blossoms, but also many delicious new fruits. ”

“ The possibilities of the pedigree-culture are by no means exhausted with covering the above points, especially if the plants chosen for the objects happen to be capable of vegetative reproduction, that is by cuttings or slips, in which case comparisons should be made of progenies grown from seeds of the plant with wide leaves with individuals grown, from slips of the same, and also compared with others from the extreme end of the series. ”

“ If we now consider the crossed and self-fertilised plants of the three generations, we find an extraordinary diversity in their relative heights. In the first generation, the crossed plants were inferior to the self-fertilised as 100 to 178; and the flowers on the original parent-plants which were crossed with pollen from a distinct plant yielded much fewer seeds than the self-fertilised flowers, in the proportion of 100 to 150. ”

“ If the plant fertilizes itself without the aid of insects, as do some evening-primroses, the seed saved from the native locality may prove wholly pure, and if it does give rise to a uniform progeny the constancy of the race may be assumed to be proved, provided that repeated trials do not bring to light any exceptions. If the offspring shows more than one type, cross-fertilization is always to be looked to as the most probable cause, and should be excluded, in order to sow pure seeds. ”

“ In other words, such plants are pure bred, they lack the usually obvious virility that comes from crossing the male of one plant with the female of another. There are so many devices to prevent self-fertilization in flowers, so marvelous are the contrivances to see to it that only cross-fertilization can be effective, and, finally, the experience of breeders that strength and virility often or usually result from impregnating the ovules of one plant with the pollen of another, that we are forced to the conclusion that absolute purity in the sexual relations of flowers is rare indeed. ”

“ By Seeds.—This may be called the natural means of increasing the number of any particular kind of plant, but it is to be remembered that we do not by that means secure an exact reproduction of the parent, especially in the case of plants raised or evolved in the course of generations by hybridization and selection. We may get a progeny very closely resembling it, yet each plant possessing a distinct individuality of its own; or we may get a progeny very unlike the parent, or a mixed progeny showing various degrees of divergence. Many seeds will grow freely if sown in a partially ripened state ”

“ Here the rule prevails that every plant must be fertilized with pollen of its own, or with pollen of other individuals of known and recorded origin. The visits of insects must be guarded against, and no seeds should be saved from flowers which have been allowed to open without this precaution. Then the seeds of each individual must be saved and sown separately, so as to admit of an appreciation, and if necessary, a numerical determination of the nature of its progeny. And last but not least the experiments should be conducted in a similar manner during a series of successive years. ”

“ Doubleness is strongly inherited. No one has produced, as Lindley remarks, [97] double flowers by promoting the perfect health of the plant. On the contrary, unnatural conditions of life favour their production. There is some reason to believe that seeds kept during many years, and seeds believed to be imperfectly fertilised, yield double flowers more freely than fresh and perfectly fertilised seed. [98] Long-continued cultivation in rich soil seems to be the commonest exciting cause. ”

“ 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. ”