'58 



SOME OP THE PRINCIPLES OP PLANT- BREEDING 



that ordinarily like begets like, but it is also true 

 that like frequently gives rise to unlike. There are 

 thus apparently two conflicting principles in plant- 

 breeding. On the one hand, the breeder seeks to 



Fig. 78. Individuality in cotton bolls. Smooth seeds above 

 and fuzzy ones below, from four bolls of one hybrid plant. 



produce variations in order to get new types as the 

 foundations for improvement. On the other hand, 

 when such a variation from or improvement on the 

 normal type is secured, he then reverses the pro- 

 cess and tries to establish heredity and reduce the 

 amount of variation, so that the aphorism, "like 

 begets like," will hold true. 



In pedigree or grade breeding, and in breeding to 

 produce new varieties, the importance of hereditary 

 strength, prepotency or transmitting power, cannot 

 be overestimated, as it is only by rendering this 

 power very great that any new form can be brought 

 to what is called a fixed type. 



Unity of individual. — The unity of the individual 

 is also an important factor in plant-breeding. If, 

 for instance, the breeder is attempting to produce 

 a seedless fruit, it is important that he discover 

 the tendency to seedlessness in the entire individual. 

 It would not be the correct policy for a breeder to 

 select simply a single fruit which might acciden- 

 tally be, nearly seedless. He should examine a large 

 number of fruits of different individual plants, and 

 find a plant on which he can discover a general 

 tendency toward seedlessness showing in all of the 

 fruits produced. By selecting seed from such indi- 

 viduals, he may be able to find in time one such 

 individual that would transmit to its progeny this 

 tendency to produce few seeds. 



While this is certainly generally true, there are 

 some instances in which divisions of the individual 

 are important. As an illustration may be mentioned 

 the case of hybrids between a smooth- and a fuzzy- 

 seeded cotton : when one is breeding to produce a 

 smooth, black seed, it may be desirable to select a 

 part of an individual. In this case the writer has 

 found that very frequently a cotton hybrid of the 

 above parentage will produce bolls that vary greatly 

 in the amount of fuzziness on the seed, and that this 

 variation does not seem to be limited to any part of 

 the plant in particular, but seems to be a variation 

 jn certain branches or bolls (Pig. 78), and is thus a 



sort of bud variation. The writer's experiments 

 have shown that by taking seed from certain bolls 

 in which the seeds are nearly smooth and black, a 

 much larger number of plants is produced the 

 next year with smooth black seeds than are pro- 

 duced when bolls are selected in which the seeds 

 have considerable fuzz, although the seed in both 

 cases were borne on the same plant. This illustra- 

 tion shows that in some instances it is desirable to 

 select a certain fraction or part of an individual 

 which shows more clearly the character desired. 



Variations. — It is well known that all plants 

 vary. Plants differ from each other just as do men. 

 Each plant has a facial expression, as it were, which 

 marks it as distinct from any other plant of the 

 same variety (Pig. 79). These slight fortuitous 

 or individual variations are of the greatest value 

 to the plant-breeder in connection with what may 

 be termed pedigree breeding. By these variations 

 alone, however, we would not expect to produce 

 strikingly new varieties. 



A second type of variation which is of value to 

 the breeder is those known as " sports," or muta- 

 tions (Pig. 80). These difl'er from individual vari- 

 ations only in degree. They are what may be termed 

 large-type variations, and ordinarily reproduce true 

 to seed. A very large number of our new races and 

 varieties of cultivated plants are the results of such 

 mutations or seedling sports. All vegetable-growers 

 know that far the larger number of their new varie- 

 ties are apparently produced suddenly. For instance, 

 Livingston, who has bred a great many new varie- 

 ties of the tomato, followed the practice of examin- 

 ing carefully his different plants for variations. 

 Occasionally some striking new type differing from 

 other varieties would be found. This was selected 

 and used as the foundation stock for a new variety. 

 Our good apples, pears, and peaches, have been found 

 in many cases in fence-corners, and new varie- 

 ties of wheat, cotton and other crops have resulted 

 very largely from the selection of strikingly good 

 plants which, because of their superior quality, 



Fig. 79. Variation. Differences between tobacco plants, in 

 size, shape of leaves, and also in time of maturing. 



have attracted the attention of growers, and have 

 been propagated. While many of these accidental 

 discoveries are doubtless of hybrid origin, still it is 

 probable that the majority are simply mutations or 

 sports. 



