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SCIENCE 



[3Sr. S. Vol. XXXVII. No. 961 



tion. Examples of them have just been 

 seen in the colors of flowers or of plumage, 

 and in the structure of the wings in flies. 

 Their interest lies especially in the fact 

 that they are transmitted independently of 

 one another, as if they were separate and 

 independent things. By appropriate cross- 

 ing experiments, such as we have just seen, 

 particular groups of such characters may 

 be split up and recombined, over and over 

 again, in constantly new combinations, 

 with no alteration of their individual char- 

 acter. Let us look at one or two examples 

 of this. Here are the results of crossing 

 two different races of wheat (from experi- 

 ments by Biffen) . One parent is a bearded 

 variety with short, dense heads; the other 

 a beardless form with long, loose heads. 

 The hybrid is intermediate in shape, and is 

 beardless. On pairing the hybrids together 

 all combinations of the four original char- 

 acters, and of the hybrid character, appear 

 in the grandchildren, namely, (1) short 

 beardless, (2) short bearded, (3) hybrid 

 bearded, (4) hybrid beardless, (5) long 

 bearded and (6) long beardless. These 

 six types appear in definite numerical 

 ratios, and it is evident that the bearded 

 or beardless character has been trans- 

 mitted quite independently of the shape of 

 the head. 



Another and very striking case of the 

 same kind is here seen, again from Mor- 

 gan's experiments on fruit-flies. The 

 grandfather has white eyes and yellow 

 body color; the grandmother red eyes and 

 gray body color. In the first generation all 

 the offspring have red eyes and gray color. 

 Among the grandchildren, however, ap- 

 pear not only both the original combina- 

 tions but two new ones, namely, white- 

 eyed grays and red-eyed yellows. Here 

 again the second generation of hybrids 

 shows all possible combinations of the four 

 original unit-characters, white eye, red 

 eye, yellow color and gray color. With a 



larger number of unit-characters the same 

 would hold true, but the number of combi- 

 nations would be much larger. 



"We catch a glimpse here of the methods 

 by which the modern breeder of plants or 

 animals is able to break up known combi- 

 nations and recombine them into new 

 types, somewhat as the organic chemist 

 splits up known organic compounds and 

 recombines the products into new com- 

 pounds, perhaps unknown before. Our 

 ability to do this is often of high practical 

 value. As de Vries has said, most hybrids 

 owe their character to a new combination 

 of qualities. "It is the combination that 

 is new," he says, "not the qualities them- 

 selves. Some characters are derived from 

 one parent, others from the other. Each 

 of these may be simply inherited, . . . but 

 by their new combinations they yield va- 

 rieties of higher practical value, and 

 notable examples are afforded in those 

 cases where one parent has contributed 

 vigor of growth, hardiness in winter, re- 

 sistance to disease or productivity, and the 

 other bright flowers, palatable fruit or 

 nutritive seeds." An example of this 

 which he cites is Luther Burbank's cele- 

 brated white blackberry, produced syn- 

 thetically by uniting in one race the light 

 color of the fruit of an inferior variety of 

 cultivated bramble with the large and suc- 

 culent fruit of the Lawton blackberry. 

 Another familiar example, also cited from 

 Burbank's work, is the so-called Shasta 

 daisy, which unites the desirable qualities 

 of plants from three different continents. 

 An English daisy has contributed its large 

 flowers and tall, stiff stems; a Japanese 

 species its whiteness of bloom; an Ameri- 

 can fleld daisy its profusion of flowers and 

 hardiness in winter. Many other examples 

 might be given to illustrate how by disas- 

 sociation, recombination and selection de- 

 sirable qualities may be brought together 

 and undesirable ones eliminated; and by 



