— i;i7 — SECTION III.

The Improvement of the Cotton Crop.

With tlio iiuTCiiiSC in ]vn<)\\'k'(lij;c of the laWK (li hrrcditN' ha.s eoiiic a. vi'vniiiitidii (vl the lact that a pemiaiicnt iiii|ii-()\-i'Uu'ut in the (|uality of u eroj) can iie\'er be obtained 1)\- .seleetion ahme.

A\ iieu (h'abiiL,' with a crop siu'h as eotton, m whieii \'icinisiii |ila\'s so i;i'eat a part, mass seh'etir))i eithei' b\' seeds oi' phiiits wonld oii]\' incj'i'ase the teudiMiey towards irreiularity, since anv appari'iit snperioi'ity is usiialh- (hie to cross fertlhsation. If coiitainiiiatioii fi'oiu oiitsiih' sciiii'ces were e,\elnih'<l, and pure parents wei'e eniployeih. ini[iro\'enient of a. teni[)oi'ai'\' nature niii;lil, bi; expected by the sek'ctiou of the most desirable plants and the sowing of the se(.'d i-esultini; therefrom.

The coinmei'cial cotton crop is, howe\'er, a hetei'ogeneous colh'cfion of hybriiis (ierncd from \'arioiis soui'ces, the nrdi\'idual characteristics of which segregate in accordance with the simple laws of heredity.

In order that the futility of mass selection in the presence of cross fertilisation nuiy be appreciated, a brief statement will lie made of Mendel's law.

The fundamental fact on wdiich this law is basetl is the conce[ition of individuals as composed of unit characters which are transmittetl intact. Whenever mating occurs between a pair of indivitluals, each separate unit character blends with a corresponding character, producing a hybrid wdiich resembles either parent according as one is dominant over the other.

The hvbrid on being propagated, splits, and the characters of the I'esulting progeny segregate in the definite ratio f : L' : 1, or judging from the external appearance only, in the ratio 3:1.

A simple illustration will render this clear, and also illustrate the necessity for dealing with unit cliaracters separately.

If a white-flowered is crossed with a yellow-flowered cotton the resulting hybrid is yellow, owing to the fact that yellow is " dominant '' aiul wdnte " recessive."

Y < w IYW (hybrid yellow in appearance) When this liybrifi reproduces, segregation occurs as follows : (Velluw) YY YW YW v,-\\- (White) I YeHow I YY I WW I I I YY 2 YW WW The pure forms yy and wwv wall breed pure, but the impure yw will continue to split as long as it is projjagated. It is assumed, oi course, that vicinism or natural crossing is excluded.