You will understand this fully if you read carefully Sections XIV-XVI. Since the seed is made of two plants, the plant that springs from a seed is much more likely to differ from its mother plant, that is, from the plant that produces the seed, than is a plant produced merely by buds. In some cases plants "come true to seed" very accurately. In others they vary greatly. For example, when we plant the seed of wheat, turnips, rye, onions, tomatoes, tobacco, or cotton, we get plants that are in most respects like the parent plant. On the other hand the seed of a Crawford peach or a Baldwin apple or a Bartlett pear will not produce plants like its parent, but will rather resemble its wild forefathers. These seedlings, thus taking after their ancestors, are always far inferior to our present cultivated forms. In such cases seeding is not practicable, and we must resort to bud propagation of one sort or another.
While in a few plants like those just mentioned the seed does not "come true," most plants, for example, cotton, tobacco, and others, do "come true." When we plant King cotton we may expect to raise King cotton. There will be, however, as every one knows, some or even considerable variation in the field. Some plants, even in exactly the same soil, will be better than the average, and some will be poorer. Now we see this variation in the plants of our field, and we believe that the plant will be in the main like its parent. What should we learn from this? Surely that if we wish to produce sturdy, healthy, productive plants we must go into our fields and pick out just such plants to secure seed from as we wish to produce another year. If we wait until the seed is separated from the plant that produced it before we select our cotton seed, we shall be planting seed from poor as well as from good plants, and must be content with a crop of just such stock as we have planted. By selecting seed from the most productive plants in the field and by repeating the selection each year, you can continually improve the breed of the plant you are raising. In selecting seed for cotton you may follow the plan suggested below for wheat.
Figs. 49 and 50. Chrysanthemums and Asparagus
The difference that you see between the wild and the cultivated chrysanthemums and between the samples of asparagus shown in Figs. 49 and 50 was brought about by just such continuous seed-selection from the kind of plant wanted.
Fig. 51. Two Varieties of Flax From One Parent Stock
By the careful selection of seed from the longest flax plants the increase in length shown in the accompanying figure was gained. The selection of seed from those plants bearing the most seed, regardless of the height of the plant, has produced flax like that to the right in the illustration. These two kinds of flax are from the same parent stock, but slight differences have been emphasized by continued seed-selection, until we now have really two varieties of flax, one a heavy seed-bearer, the other producing a long fiber.
You can in a similar way improve your cotton or any other seed crop. Sugar beets have been made by seed-selection to produce about double the percentage of sugar that they did a few years ago. Preparing and tilling land costs too much in money and work to allow the land to be planted with poor seed. When you are trying by seed-selection to increase the yield of cotton, there are two principles that should be borne in mind: first, seed should be chosen only from plants that bear many well-filled bolls of long-staple cotton; second, seed should be taken from no plant that does not by its healthy condition show hardihood in resisting disease and drouth.
The plan of choosing seeds from selected plants may be applied to wheat; but it would of course be too time-consuming to select enough single wheat plants to furnish all of the seed wheat for the next year. In this case adopt the following plan: In Fig. 52 let A represent the total size of your wheat field and let B represent a plat large enough to furnish seed for the whole field. At harvest-time go into section A and select the best plants you can find. Pick the heads of these and thresh them by hand. The seed so obtained must be carefully saved for your next sowing.