SOME OP THE PRINCIPLES OP PLANT- BREEDING 



67 



need be given no attention. The knowledge of 

 Mendel's principles may not change greatly the 

 practical methods of breeding which have been 

 followed for a number of years, but they give us a 

 more thorough comprehension of what we are do- 

 ing, and also greater surety that certain combina- 

 tions of parental characters can be secured. 



(2) The use and fixation of intermediate or blended 

 types. 



The principle of the purity of the germ-cell, if 

 strictly applied, would not recognize as possible 

 the fixation into a race reproducing true to type 

 of an intermediate hybrid, that is, one in which 

 two characters of a certain pair are blended. Yet 

 practical work show's that such a fixation certainly 

 can be secured. In very many hybrids of plants 

 cultivated for their fiowers, intermediate colors 

 have been bred to stability, showing that the 

 inheritance is blended. The writer has been at- 

 tempting to fix a hybrid of Black Mexican sweet 

 corn having blue-black kernels, with Stowell's 

 Evergreen, which has a nearly white kernel, into 

 a race of light blue-violet color, and strictly inter- 

 mediate in this respect between the two parental 

 varieties. Ordinarily, the color of these hybrids 

 breaks up in Mendelian proportions, but neither 

 color can be considered to be dominant in the true 

 sense of the word. In practically all cases when 

 the potentialities of the two characters are mixed 

 in the same egg-cell, the coloration is intermediate 

 rather than like one or the other of the parent vari- 

 eties. The writer has uniformly selected the seed 

 of such intermediate light blue-violet kernels for 

 planting, and has kept the patch completely iso- 

 lated. After four years of such selection, a type 

 that produces nearly uniformly light blue colored 

 kernels has been produced. There are still many 

 reversions to the coloration of either parent, but 

 these are growing fewer and the type is becoming 

 fixed into a stable race, reproducing itself true 

 to seed. Halsted, of the New Jersey Experiment 

 Station, has produced such an intermediate colored 

 race by the hybridization of Black Mexican with 

 the Egyptian, and has already secured a new race 

 which is practically fixed in its intermediate color. 

 The writer thinks that in this and in a great many 

 other cases it is possible by careful selection of 

 plants showing the intermediate type to breed new 

 races that exhibit a blend of characters, and such 

 blends are frequently of great value. 



The work that has been carried out by the 

 writer in the Department of Agriculture in the 

 breeding of citrous fruits very clearly indicates 

 that valuable intermediates may sometimes be 

 secured. The writer, in conjunction with Mr. 

 Walter T. Swingle, hybridized the hardy, cold- 

 resistant trifoliate orange (Citrus trifoliata) with 

 several varieties of the tender sweet orange, and 

 as a result at least five different varieties of 

 hardy oranges or citranges have been produced 

 (Fig. 86). These hybrids are nearly intermediate 

 between the two parents, having the characters in 

 the first generation nearly blended. The leaves are 

 trifolioliate, but are much larger than the leaves of 



the ordinary trifoliate orange tree, and show a 

 tendency to drop off, the lateral leaflets producing 

 an unifolioliate leaf. The trifoliate orange is decid- 

 uous, while the sweet orange is evergreen. The hy- 

 brids are semi-deciduous, holding a large share of 

 their leaves through the winter. In hardiness they 

 also seem to be intermediate, being much more 

 cold-resistant than the ordinary orange, but not 

 so hardy as the trifoliate orange. They are suffi- 

 ciently hardy so that they doubtless may be grown 

 with safety as far north as South Carolina, or 300 

 to 400 miles north of the present orange region. 

 Some of the fruits produced are as large as the 

 ordinary orange, but the majority are very nearly 

 intermediate in size. They are very variable, how- 

 ever, in the first generation. At least five of 

 the fruits that have been produced are juicy and 

 valuable. It is not probable that they would be 

 reproduced true to seed, but orange varieties are 

 clons, and the different types will, of course, be 

 normally repro- 

 duced by buds or 

 grafts, so that 

 from a practical 

 standpoint it does 

 not matter 

 whether or not 

 they would repro- 

 duce true through 

 the seed. In the 

 second generation 

 it is prob&ble that 

 these different 

 characters would 

 split up, possibly 

 according to Men- 

 del's law, and it 

 is likely that still 

 more valuable va- 

 rieties will be 

 secured when a 

 second generation 

 has been grown. 

 Similar groups of valuable intermediate types of 

 fruits have been produced by Dr. Saunders, the 

 Director of the Canadian Experimental Farms, by 

 crossing varieties of the ordinary apple, such as 

 the Pewaukee and Wealthy, with a very hardy 

 cold-resistant crab (Pyrus baeeata). Dr. Saunders 

 has produced already numerous hardy intermedi- 

 ate types which bid fair to be of very great 

 economic value. 



(3) The combination of different parental characters 

 not blended. 



The greatest value of hybridization in the pro- 

 duction of new varieties lies probably in the possi- 

 bility of combining in the new race certain valu- 

 able characters of different races or species. This 

 principle breeders have long recognized, but it 

 cannot be too clearly borne in mind. The work 

 which the writer has carried out in the Department 

 of Agriculture, in the production of long-staple 

 varieties of upland cotton, forms an interesting 

 illustration in point. Ordinary upland cotton, 



Fig. 86. Valuable intermediate orange 

 hybrids, and the parents, o, com- 

 mon orange; 6, trifoliate orange; 

 c, Willits citrange (trifoliate X 

 orange) ; d, Morton citrange (tri- 

 foliate X orange) ; e. Busk citrange 

 (orange X trifoliate) . 



