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crops, just as there now are many breeders of pure strains of domestic animals.
38. Methods of Improvement. — There are three steps or methods in the improvement of plants or animals, viz.:
A. Inducing variation.
C. Testing the power of specific forms to reproduce themselves.
39. A. Inducing Variation.—Variation is the basis of selection. Plants must vary or they could not be selected. There are two general methods of producing variations, viz.:
1. Environment, such as soil, climate, space, cultivation, etc. 2. Crossing.
40. The Influence of Environment.—The causes of variability cannot be discussed here, but the following facts should guide the breeders of plants.
1. Horticulturists do take advantage of a superabundance of food in causing modification or multiplication of parts, such as the development of petals from stamens. After this habit becomes fixed it will be transmitted in some measure even in poor soil.
2. Nevertheless the most important value of cultivation in the case of most plants is to allow the plant breeder or cultivator to study individual forms. It enables him to select the desirable forms and reject the undesirable ones. By milking the cow and testing her milk we are able to select the best milkers. By trotting horses we are enabled to breed those best able to trot. Whatever influence milking or trotting may have, the fact remains that it makes possible intelligent selection.
3. The variations selected should be those induced under the environment in which we expect to continue to grow the crop. If we expect to grow three stalks of maize to the hill in general field culture, it is desirable to select the ears for planting from maize grown in a similar manner, rather than from ears
where but one stalk is grown in a hill. In the latter case the size of the ear will not be a criterion of the size of the ear where three stalks are grown in a hill. Where it is not possible to make selection under field conditions, care should be taken to select from among plants under like environment and subsequently subject to field conditions.
“In selecting sugar beets,” says Vilmorin,1 “ those roots are sought for that are straight, long, and free from lateral branches. This is right, for those that are branched are more difficult, and hence more expensive, to gather. Now, certain growers of beet seed in the north of France once formed the idea-thinking, no doubt, in this way to improve their varieties—of growing the plants which were to be used as seed stocks in very rich deeply worked soil where they were very much crowded together; so much so that 16 to 20, or even more, grew on one square meter of ground. The result was that the beet assumed the form, and later the length of a whipstock. They were not branched because the roots were very closely crowded together. Their sugar content was abnormally high as a result of their growing so close together, and the conclusions drawn from the form of the roots and their sugar content, as determined in the laboratory, were tainted with error because they did not represent qualities truly acquired, but modifications accidentally imposed by external conditions. Thus these beets which were declared to be of good shape and composition in the laboratory yielded seed which when sown in the open field, produced branched roots of only moderate sugar content, because the descendants had reassumed their true characters when they were released from the restraint which had been artificially imposed upon the parent plants.”
41. Change of Seed.—A frequent change of seed is not necessarily a good thing; certainly it is not necessary to obtain seed from distant parts of the country for a region whose soil and climate are well suited to the crop. If the region is not well adapted to the crop frequent new supplies of seed may be helpful and even essential. Probably no part of the world is better adapted to maize than is much of the central Mississippi valley. There would seem to be no good reason for changing seed of maize in this region. Much of this same region is not equally well suited for the oat crop. The climate is too hot and dry. The oats are much lighter than those produced in more moist and cool regions. Obtaining seed oats from regions where the crop does better may be good business management.
1 E. S. R., Vol. XI, p. 13.
42. Crossing.-- Crossing two unlike forms or two varieties may not be a fundamental cause of variation. Some other cause must have operated to have produced the two unlike forms. In practice, however, crossing is a means of inducing variation, so as to enable the breeder to select forms more nearly suited to his ideal. This is shown by Hays? in the case of a hybrid between Fife and Blue Stem wheat.
Some of the plants of hybrid wheat yielded more and. some less than any of the plants of either the Fife or of the Blue Stem. If the yield is the character
Influence of crossing as a cause of variation. istic desired, then a few
Yield in grains of 100 plants, showing greater plants of the hybrid variation in yield of hybrid wheat than of either were better than either parent form. The yield of the hybrid is indicated
by the line marked -x- (After Hays.) of the present varieties.
Crossing is also employed not only to induce variation but to combine two or more desirable qualities in one plant.
43. B. Selection.—Plants having varied either through the efforts of the breeder or otherwise, the next step is to select plants having the characteristics desired. “Selection is the surest and most powerful instrument that man possesses for the modification of living organisms."2
The unit of selection is the .ndividual. In the case of wheat the unit is not the seed, nor even the head of the wheat, but it is the stool containing several heads and many seeds which have been produced from a single seed. In the case of the potato it
is the single hill and not the single potato. However, in plants, . unlike higher animals, portions may be used for the purpose of
Willet M. Hays. Plant Breeding. Division of Vegetable Physiology and Pathology, U. S. Department of Agriculture, Bul. 29, p. 21.
9 Henry L. De Vilmorin. E. S. R., Vol. XI, p. 19.
reproduction and the inheritance of variations in these parts is recognized as possible.
Only useful characters should be selected, because two characters are more difficult to develop than one; three more difficult than two, . and so on. Some characters are mutually antagonistic, as extreme earliness and either great size or productiveness. To select wisely requires deep study and good judgment. Varieties frequently deteriorate on account of unwise selection. This is especially true of maize, although it is the field crop which it is the easiest to select.
44. C. Testing Power of Specific Forms to Reproduce Themselves.-Having selected a desired form, it is next necessary to test its ability to transmit its characters. Even though the sire (plant furnishing the pollen) may be known, there is no certainty that the plant will transmit the characters which it possesses. Different grains from the same head of wheat are known to yield unequally. Some variations are easily fixed : others require generations of selection before the characters can be depended upon. Under ordinary farm conditions the ability of individuals to reproduce themselves is not tested, and furnishes a very important reason why little progress has been made in the improvement of field crops. Take timothy, for example. A casual inspection of a field of timothy will show that there is a great variation in the length of head, the length of stem, the amount of leaves and number of stalks per stool. Under the usual method no selection is exercised, and no test of the power of the transmission of characters is possible. A few experimenters have selected plants (stools) having different character. istics and by planting 100 seeds from each plant in rows, one seed at a place, have obtained remarkable results. After the ability of the plant to transmit its characters has been demonstrated, the seed can be rapidly multiplied for field purposes.
It is well understood by livestock breeders that the best individual does not always produce the best progeny. It is a
common expression that this animal is a good breeder or that animal a poor breeder.
At the Ohio State University in 1902, fourteen ears of maize of a given variety were selected, and two rows of fifty hills each were planted from each ear. The smallest ear, containing next to the smallest weight of maize, produced the heaviest yield of maize. This ear weighed 14 per cent less than the average weight of the fourteen ears and yielded 32 per cent more than the average yield of the same fourteen ears. This testing of the power of plants to transmit their characteristics is painstaking work, and will form a large part of the work of the successful plant breeder.
45. Importance of Large Numbers. If a thousand persons stand in a row it will be found that most of them are nearly the height of the average, while a few are considerably shorter and a few considerably taller than the average. The length or weight of a number of ears of maize will vary in the same manner as shown in wheat. (42) In fact this seems to be a universal law of organic beings. Most of them tend to breed true to type: a few vary considerably from the type. In order, therefore, to make progress in breeding it is necessary to find the organisms that have the tendency to vary as desired. Among a million organisms there may be only one that possesses the required characteristics. The chances of finding the desired individual increase as we increase the number from which selection is made. The chances of securing satisfactory results are increased many fold if 5000 seeds are planted instead of 500.
46. The Plant Breeder's Advantage.--It has been shown that the breeder of animals has the advantage of the breeder of plants in that he can more easily control the mating of the parents. The breeder of plants has a distinct advantage in being able to work with large numbers.
In the case of livestock only the inferior females can be discarded, because in working with adults the expense of discarding