PLANTS, Breeding of. Fundamental Prin ciples.— Only the most limited view of plant breeding can be given in an ordinary thesis. It would be necessary to extend the subject through many volumes to give even a general view of what has already been demonstrated, and that which the clear light of science has yet to bring forth from the depths is too extensive even for the imagination to grasp, except through a full knowledge of what practical field-work has already accomplished.
The fundamental principles of plant-breed ing are simple, and may be stated in few words; the practical application of these principles de mands the highest and most refined efforts of which the mind of man is capable, and no line of mental effort promises more for the eleva tion, advancement, prosperity and happiness of the whole human race.
Every plant, animal and planet occupies its place in the order of Nature by the action of two forces — the inherent constitutional life force with all its acquired habits, the sum of which is heredity; and the numerous compli cated external forces or environment. To guide the interaction of these two forces, both of which are only different expressions of the one eternal force, is, and must be, the sole object of the breeder, whether of plants or animals.
When we look about us on the plants inhab iting the earth with ourselves, and watch any species day by day, we are unable to see any change in some of them. During a lifetime, and in some cases perhaps including the full breadth of human history, no remarkable change seems to have occurred. And yet there is not to-day one plant species which has not undergone great, and to a certain extent con stant change.
The life-forces of the plant in endeavoring to harmonize and adapt the action of its ac quired tendencies to its surroundings may, through many generations, slowly adapt itself to the necessities of existence. yet these same accrued forces may also produce sudden, and to one not acquainted with its past history most surprising and unaccountable. changes of char acter. The very existence of the higher orders of plants which now inhabit the earth has been secured to them only by their power of adap tation to crossings, for through the variations produced by the combination of numerous ten dencies, individuals are produced which are bet ter endowed to meet the prevailing conditions of life. Thus to Nature's persistence in cross
ing do we owe all that earth now produces in man, animals or plants; and this magnificently stupendous fact may also be safely carried into the domain of chemistry as well, for what is common air and water but Nature's earlier ef forts in that line, and our nourishing foods but the result of myriad complex chemical affinities of later date? Natural and artificial crossing and hybridi zation are among the principal remote causes of nearly all otherwise perplexing or unaccount able sports and strange modification, and also of many of the now well-established species. Variations, without immediate antecedent cross ing occur always and everywhere from a combi nation of past crossings and environments, for potential adaptations often exist through gener ations without becoming actual, and when we fully grasp these facts there is nothing myste rious in the sudden appearance of sports; but still further intelligent crossings produce more immediate results and of great value, not to the plant in its struggle with natural forces, but to man, by conserving and guiding its life-forces to supply him with food, clothing and innumer able other luxuries and necessities. Plant-life is so common that one rarely stops to think how utterly dependent we are upon the quiet, but magnificently powerful work which they are constantly performing for us.
It was once thought that plants varied within the so-called species but very little, and that true species never varied. We have more lately discovered that no two plants are ever exactly alike, each one having its own individuality, and that new varieties having endowments of priceless value, and even distinct new species, can be produced by the plant-breeder with the same precision that machinery for locomotion and other useful purposes are produced by the mechanic.