68 



SOME OP THE PMNCIPIJ!S OF PLANT -BREEDING 



which is grown all over the interior' cotton regions 

 of the South, produces a short fiber averaging 

 about one inch in length. In the eastern part of 

 South Carolina, southern Georgia and northern 

 Florida, sea island cotton is grown. This cotton 



Fi£. 87. Selection. Kesults of ro^ueing in a verbena seed-ileld. 



has a fiber If to 2J inches in length. Ordinary up- 

 land cotton has an average value of eight or nine 

 cents per pound, while this longer staple sea island 

 cotton is ordinarily worth twenty to thirty cents 

 per pound. Other things being equal, a longer- 

 fibered cotton is always more valuable than a short 

 staple, and were it possible to secure the same 

 yield it would be far better to grow long-staple 

 cotton altogether. The sea island or long-staple 

 cotton, however, has a small three-locked boll 

 which opens very poorly, and is difficult to pick, 

 and yields much less than does upland cotton. Up- 

 land cotton, on the contrary, produces large rounded 

 bolls, which open wide and are easy to pick, and 

 yields much more heavily than the other. Sea 

 island cotton has a smooth black seed, so that rol- 

 ler gins can be used in separating the seed and 

 fiber, and this is an important consideration with 

 long-staple cotton, as the saw-gin tears and breaks 

 the fiber. With the short-staple or upland cottons 

 the seed is covered with a short close fuzz, and 

 they are uniformly ginned on saw-gins. The tear- 

 ing of the fiber which necessarily results to a con- 

 siderable extent, does not matter greatly with a 

 fiber of this short length. If longer stapled varie- 

 ties are desired they should have smooth, black seed, 

 so that a roller gin can be used. The writer under- 

 took experiments in the hybridization of these two 

 kinds of cotton, in the hope of producing a new 

 race, which would inherit, on the one hand, the 

 large bolls, tendency to yield heavily, and adapta- 

 bility to upland regions, of the short -staple or 

 upland cotton, and, on the other hand, the long, fine 

 and strong lint and black seed of the sea island cot- 

 ton. The first-generation hybrids were found to be 

 nearly uniform and showed little breaking up of 

 characters of the two parents. In the second gene- 

 ration, however, all manners of types were formed, 

 exhibiting the characters of the two parents in 

 very different degrees. Out of several thousand 

 second-generation hybrids several individuals were 

 selected which showed almost exactly the combi- 

 nation of characters which it was desired to pro- 

 duce. These hybrids were self-fertilized the next 



year, and each one was planted in an isolated patch 

 in order that it would be fertilized only with 

 pollen of related progeny. In each generation since, 

 only those plants have been selected for seed which 

 come the nearest to the original type, and now, 

 after five generations of selection, two or 

 three of the types have been bred to a 

 practical state of fixity, showing the pos- 

 sibility of combining in a hybrid valuable 

 characters from distinct parents. 



,(4) Fixation of hybrids. 



When different types have been crossed 

 and hybrids secured which possess the char- 

 acters desired, it is necessary that careful 

 methods of selection and breeding be fol- 

 lowed in order to secure finally a type that 

 will transmit its qualities. The great ma- 

 jority of such hybrids when first produced 

 will not reproduce true to type. The policy 

 followed by the writer in the cotton ex- 

 periment above referred to, will usually serve as 

 a good guide in the fixation of any hybrid. If self- 

 fertile, the hybrids should be fertilized with their 

 own pollen in order not to introduce any new hered- 

 itary tendencies unless it is found that such fer- 

 tilization too greatly reduces the vigor. In cotton, 

 self-fertilization has been found not to decrease the 

 vigor of the plants, and the same is true of wheat, 

 tobacco, oats, and plants that are normally self- 

 fertilized to some extent. In the case of corn, as it 

 has been found that the inbreeding of a plant with 

 its own pollen results in a great deterioration in 

 vigor, it is the best policy to cross the desired 

 hybrid with another hybrid having the same char- 

 acters. The seed of such select hybrid plants should 

 then be planted in isolated places, so that the plants 

 will not be crossed with the pollen of either parent 

 or other varieties. When the progeny of these select 

 hybrids reach a point where their characters be- 

 come visible it may be desirable to weed out the 

 undesirable plants that are off type, in order that 

 the plants which most nearly resemble the type 

 desired will be fertilized with pollen from similar 

 plants. In the writer's cotton experiments, the 

 seed of each individual selected plant of the second 

 generation was planted in. a small isolated plot of 

 about one acre. As soon as the plants began to 

 show their characters and it could be recognized 

 that certain ones had inherited the desired qualities, 

 the fields were carefully searched and all plants 

 not true to type were pulled up, leaving only a few 

 good plants of the right type. (Fig. 88.) This in- 

 sured that all of the later bolls formed would be 

 fertilized with pollen from similar plants of good 

 type. Each subsequent generation, the select plants 

 should be grown in isolated plots and seed selected 

 only from those plants which have reproduced the 

 ideal type for which the breeder is working. 



The time required to secure fixed types is 

 variable, but in wheat and cotton, when careful 

 experiments have been carried out and recorded, 

 the indications are that four to six generations are 

 ordinarily required to reach a fixed stage. This 

 does not mean, of course, that all variation is 



