1364 



PLANT -BREEDING 



PLANT -BREEDING 



How valuable this factor of environment is in the origi- 

 nation of newly cultivated sorts yet remains to be dem- 

 onstrated scientifically, but some practical plant-breed- 

 ers contend that it is a factor of very great importance. 



1839. Diagram illustrating method of selecting cotton. 



Occasionally individuals "sport," as gardeners say, 

 and plants entirely different from the type of the race 

 are produced. These variations are usually very marked 

 ones and no definite cause for their appearance is yet 

 known. Many valuable races of cultivated plants owe 

 their origin to variation of this sort. For instance, the 

 Cupid type of the sweet pea, a dwarf race, originated 

 as a seedling sport from the Emily Henderson, an ordi- 

 nary tall sort, and certain other sweet peas, the writer 

 is informed, show a tendency to sport in this way. 

 Another variation of similar kind is the change in 

 character of certain parts or branches of individuals, 

 known as bud-sporting. Bud-sports have proved par- 

 ticularly valuable in producing new sorts of chrysan- 

 themum and other plants cultivated for their flowers. 

 There appears to be no way in which the breeder can 

 induce seedling- or bud -sports, and the only course 

 seems to be to watch carefully for their occurrence and 

 be ready to utilize them whenever they appear. 



The most fertile way of securing variations is by the 

 intermingling of species and varieties by hybridization. 

 By blending distinct types of different species or races 

 in this way, individuals of almost any grade of inter- 

 mediacy between the two parents can be obtained and 

 those having valuable combinations of characters se- 

 lected and sometimes fixed into stable races. Cross- 

 ing in general is probably the most active agency in 

 procuring variation, and is thus of the highest impor- 

 tance to the plant-breeder, inasmiich as the production 

 of the initial variation of a desired kind and in a de- 

 sired direction is the most difficult achievement. 



Improvement by Selection. — Improvement by selec- 

 tion depends u])on the principle of gradually augment- 

 ing a quality by selecting seed each year from that 

 individual which by comparison with numerous other 

 individuals is found to exhibit the character desired in 



1840. Improvement of Sea Island Cotton by selection. 



Ordinary type on left, and selected type on rijilit. 



the greatest perfection or highest degree. By this con- 

 stant selection of seed from the best individual, it has 

 been found that the desired quality can be secured in 

 more and more marked degree the longer the selection 

 is continued. It is to this cumulative power of selec- 



tion that the great improvement in many of our cul- 

 tivated plants is due, and, in general, selection may 

 be considered a fundamental factor in the successful 

 cultivation of any crop, as it is necessary not only to 

 improve a race but to retain it true to type and in vig- 

 orous productive condition. 



The most marked instance known to the writer of the 

 improvement of a plant by selection alone and the de- 

 pendence of an entire industry on this factor, is that of 

 the sea island cotton. Every successful grower of sea 

 island cotton selects his seed each year with the great- 

 est care, and pursues year after year a definite process 

 of continuous selection. In beginning selection, the 

 general crop is examined and a number of individuals 

 selected which seem from general appearance, vigor, 

 productiveness, etc., to be superior plants. These su- 

 perior plants are then subjected to a very critical exami- 

 nation as to (1) vigor, (2) productiveness, (3) season, 

 (4) covering and size of seed, (5) character of staple, etc. 

 Under the last heading, "character of staple," attention 

 is given to (a) length, (6) strength, (c) silkiness, (d) 

 fineness, (e) uniformitj' of length and (f) proportion of 

 lint to seed. etc. Finally, considering all of the above 



1841. Improvement of corn by selection. 



Boone County White corn on left, and original type from which 

 it was developed by selection on riglit. 



points carefully, the individual which is found to be su- 

 perior to all others is selected. The seed from this is 

 saved and planted the next year in a select patch and 

 will usually yield some 500 individuals. 



The second year a single superior plant is selected 

 with the same care from among the 500 plants grown 

 from the seed of the plant selected the first year. The 

 seed of the remaining individuals of the 500 plants is 

 retained to plant a special seed patch the third year. 



The third year the seed of the specially selected plant 

 of the preceding year is grown by itself, producing 

 some 500 plants, from among which a single superior 

 individual is again selected. The seed of the remaining 

 500 plants is again retained to plant a special seed patch 

 the fourth year. Further than this, in the third year 

 the seed of the 500 plants grown the previous year is 

 planted by itself and will produce a patch of some 5 

 acres in extent, which will yield sufficient seed to plant 

 the general crop in the fourth year of the selection. 

 (Compare Fig. 18.'i9.) In succeeding years this policy is 

 continued, the general crop being grown continuously 

 from seed of a higher and higher grade of selection. 

 Under this continuous selection the quality and length 

 of the staple has been continuously imjtroved (Fig. 

 1840), and the yield increased, so that the growers to- 

 day are producing more cotton than ever before and of 

 a better quality. Corn ( Fig. 1841 ) , wheat, and very many 

 of our races of other cultivated plants have been im- 

 proved in a similar manner, and many of our most valu- 

 abl(> races to-day are simplj' types gradtially ameliorated 

 through years of continuous selection. 



In a similar manner selection may be used to improve 

 any character of a plant, as the shape or color of a 

 flower, acidity of the fruit, sugar content of the root (as 

 in the beet), protein content of the seed (as in corn and 



