Chemical selection by mechanical examination.
The method of making a chemical selection of ears of seed corn by a simple mechanical examina tion of the kernels is based on the fact that the kernel of corn is not homogeneous in structure, but consists of several distinct and readily observable parts of markedly different chemical composition. For our particular purpose of judging from the structure of the kernel as to its composition, we need consider but three principal parts, namely : (1) The darker colored and rather horny layer lying next to the hull, principally in the edges and toward the tip end of the kernel. This part, while chiefly starch, is fairly rich in protein and con tains one-half to two-thirds of all the protein of the kernel. (Fig. 644.) (2) The white starchy-appearing part occupying the crown end of the kernel and usually also immediately or partially surrounding the germ.
This part is poor in both protein and oil, consisting mainly of star-h. (Fig. 644.) 63) The germ itself, which occupies the central part of the kernel toward the tip end. This is very rich in oil. More than four-fifths of the entire oil of the kernel resides in the germ. It is also rich in protein, containing nearly one-fifth of all the protein in the kernel, although the germ itself constitutes only about one-tenth of the weight of the kernel. (Fig. 645.) In selecting seed corn by mechanical examination for improvement in composition, we remove from the ear a few average kernels, cut them into cross sections, preferably near the tip end of the kernel (see longitudinal sections), and examine these sec tions as they are cut, usually simply with the naked eye, selecting for seed those ears the kernels of which show the qualities desired.
Samples for analysis.
In order that the breeder may know what he has accomplished in his work of mechanical selection, he should have an analysis made of two composite samples representing each of the two lots of ears ; that is, the selected lot and the rejected lot. One composite sample should be made by taking ten average kernels from each of the selected ears (ninety-six ears preferred) and another sample by taking ten average kernels from each of the rejected ears (100 ears or more). Each of these two samples should be put into a separate sack, properly labeled, and sent to the chemist for analysis. Of course, if the breeder desires to breed for physical type and increased yield only, then no chemical analysis is needed, and all that is necessary to begin work is to select the ninety-six most nearly perfect ears obtainable for the breeding plot.
Size of breeding plot.
The best number of ears to use in a breeding plot is as yet an unsettled question. There are several conflicting factors entering into the con sideration. On the one hand, the smaller the num
ber of ears, the choicer can be the selection of the seed ; while on the other hand, the larger the num ber of breeding rows, the better can be the selec tion of seed for the next crop. Then, again, there is undoubtedly some danger of evil effects from too close inbreeding by the use of too small a number of ears. From our present knowledge, how ever, we think that ninety-six ears is a safe num ber to use, so far as inbreeding is concerned, and this is the number that we suggest in these direc tions, it being understood that alternate rows are to be detasseled and all seed corn selected from detasseled rows.
Planting by the row system.
The ninety-six selected seed ears are planted in ninety-six separate rows. These rows should be at least one hundred hills long, but they may well be forty rods long, as the quantity of seed will usually permit this. It is recommended that these ninety six seed ears be numbered' from 1 to 48 and from 51 to 98, the numbers 49 and 50 being omitted ; also, that ears 1 to 48 be planted in one-half of the plot and ears 51 to 98 in the other half, preferably end-to-end with the first half, leaving one hill tin planted to mark the line between the halves, and also leaving one row unplanted to mark the line between rows 24 and 25 and between rows 74 and 75, that is, between quarters. In this way, row 51 (planted with seed from ear 51) is a continuation of row 1 (planted with seed from ear 1), and the two rows may well extend eighty rods across a forty-acre field. The breeding plot can be planted with a corn-planter, although it will require some time and patience, and if the planter is an edgedrop it will be necessary to put a suitable cone or inverted funnel in each seed box to keep the small quantity of corn to the outside. Place the Ihelled corn from ear No. 1 in one box and from ear No. 2 in the other ; drive to the middle of the plot, thus planting rows 1 and 2 ; clean out the boxes ; move forward one hill ; put in the corn from ears 51 and 52; use the foot-trip till the corn begins to drop ; then drive on and plant rows 51 and 52. Turn at the end ; clean out the seed DOXOS ; put in ears 53 and 54; plant back to the middle ; clean out, put in ears 3 and 4; and then plant on back to the beginning line, thus continuing until the breeding 'These numbers would be 101 to 148 and 151 to 198 the first year, 201 to 248 and 251 to 298 the second year, etc. [See under Register number, page 425.] plot is all planted. The planting may then be con tinued for the commercial field, using the same variety of corn, which should be of similar breed ing, finishing, perhaps, with the multiplying plot on the side of the field opposite from the breeding plot.