In urging that the breeding patch be placed on the ordinary soils and cultivated under the condi tions to which the crop is to be subjected, it is not intended to convey the idea that the breeding patch should not be given careful cultivation. Slipshod methods of cultivation should never re ceive encouragement. The breeding patch should be given thoroughly good cultivation ; and such thoroughly good cultivation should also be used in the field when the crop is grown on a more exten sive scale.
Necessity of a clearly defined ideal.
Careful breeders have found it very desirable and necessary to have a clearly defined ideal type which they are striving to produce. In the selec tions within the race it is necessary that the breeder have clearly in mind all of the characters of the race which he is breeding, and the writer thinks that all breeders should be recommended to draw up carefully a description of the type which they are breeding and the objects which they are attempting to obtain, otherwise it is difficult properly to limit the selections. All breeders know that in growing a large number of plants for selection, different types that appear very promis ing are. likely to crop out here and there. We may be selecting for a certain type, and find in the row of plants which we are examining an individual that differs somewhat in its character but which s,•-ms to be of exceptional value. The temptation under such circumstances is to take this new plant and discard the old ideal. 3lanv breeders have found that by taking such selections they have made serious mistakes, and lost the improvement already secured. Whenever a plant of different character springs up it is entirely an unknown quantity, and it may not transmit the desired characters ; and, even if it should, they are differ ent from the qualities of the ideal strain for which the selection was first started.
Control of parentage.
In plant-breeding, as in animal-breeding, the isolation of the parents is a very important con sideration. It is necessary that we should know the character of both parents whenever this is possible. In breeding plants more attention is given ordinarily to the mother parent, and in very many instances the characters of the father parent are entirely neglected. Animal-breeders, on the contrary, give more attention to the characters of the male parent, and much improvement in ordi nary herds has been accomplished by the introduc tion of improved blood through the male. In plant breeding, it is desirable that the seed of the select individuals be planted in a field by themselves. This insures that only progeny of carefully selected plants will be planted near together, and thus no ordinary stock will enter as a contamination. One
can be certain that each plant of the progeny is fertilized with pollen from another similarly good plant, or at least from a plant derived from good parentage. One difficulty, however, has been ex perienced by plant-breeders in planting continu ously their selected stock in such isolated plots. If this method is continued year after year, it results in fairly close inbreeding, which in the case of plants frequently results in loss of vitality and vigor. In animal-breeding it is apparently the case that ordinarily there is no noticeable effect from close inbreeding, and many of the most famous animals have been produced as a result of the closest in-and-inbreeding. In plants, however, it is possible to secure much closer inbreeding than in the case of animals, as in many cases a plant can be fertilized with its own pollen.
Within recent years much activity has been shown in the careful breeding and improvement of corn. The corn plant has been shown, as a result of experiments made by various investigators, as, for example, by the Illinois Experiment Station and the United States Department of Agriculture, to lose vitality very rapidly when self-fertilized. (Fig. 81.) Within three or four generations, by the most careful inbreeding, it is possible to reduce corn to almost total sterility. The general practice of corn-breeders who have been giving attention to the production of pedigree strains, is to plant the rows of corn from different select ears side by side, giving a row to each select ear, and each year selecting, from the progeny of those rows which give the largest yield, plants to continue further the selection. Planting these select ears together every year, therefore, means that they are more or less inbred, as the closest relatives are planted together in the same row. While in follow ing this policy at first no effect was visible, corn breeders are now finding in some cases an appar ent decrease in yield, which seems to be traceable to the effect of inbreeding. It seems necessary for us, therefore, in corn and in other plants that are affected by inbreeding, to use methods that will avoid close inbreeding. The detrimental effect of inbreeding is largely limited to those plants which are normally cross-fertilized, this fact being strikingly brought out in Dar win's "Investigations on Cross- and Self-fertilization in the Vegetable Kingdom." Tobacco, wheat, and some other plants that are normally self fertilized do not show this decrease in vigor as a result of inbreeding. In deed, in such plants cross-fertilization ordinarily results in decreased vigor and should be avoided.