322 



SCIENTIFIC AGRICULTURE 



June, 1922 



Table V. — Factor Hypothesis for Awn Inheritance in the Cross Hard Red 

 Calcutta X Taylor's Wonder 



Short tip- 

 Almost bald awned 

 bbTt (2) bbTT (1) 

 Bbtt (2) 



Phenotype 

 Genotype 



Bald 

 bbtt (I) 



Fn plants . . 

 Observed ratio 

 Expected ratio 

 Deviation . . . 

 Probable error 

 Dev. -f- P.E. 



27 

 1.98 



1 

 0.98 

 ±0.18 

 3.4.4 



48 

 3.47 



4 

 0.53 

 = 0.32 

 1.63 



BBtt (1) 



BbTt (4) 



87 



6.33 



6 

 0.33 

 ±0.35 

 . 94, 



Long tip- 

 awned 

 BbTT (2) 

 BBTt (2) 



Bearded 

 BBTT (1) 



42 

 3.05 



4 

 0.95 

 ±0.32 

 '2.96 



16 

 1.16 



1 

 0.16 

 :0.18 

 0.89 



A cross between Hard Red Calcutta 

 (bearded) and Taylor's Wonder produced, 

 in the F2, 38 tip-awned plants and 11 beard- 

 ed. Here again a single factor difference is 

 indicated and the F., should contain three 

 classes of individuals, homozygous bearded, 

 heterozygous tip-awned, and homozygous 

 tip-awned. For reasons already mentioned 

 the two tip-awned classes were not separated. 



The cross between Hard Red Calcutta and 

 White Bobs produced, in the F,, a series of 

 forms which could be grouped with some dif- 

 ficulty into bearded, long tip-awned, short 

 tip-awned. almost bald and bald. If all the 

 bald and various tip-awned plants are placed 

 in one group and the bearded plants in an- 

 other a ratio of 15:1 is obtained and the 

 presence of two factors indicated. Consider- 

 ing then that the bearded parent contains 

 two factors. BBTT, the bald parent would 

 be represented by bbtt and a cross between 

 the two would produce the parental combina- 

 tions, and in addition, two homozygous tip- 

 awned types, BBtt and bbTT, and several 

 heterozygous types with various grades for 

 intermed'it' development of awned char- 

 acter. 



In Table V the results for the Hard Red 

 Calcutta X White Bobs cross are placed in 



five groups. The expected ratio of 1 :4:6:4:1 

 is on the basis of the genotypes which are 

 presumed to be represented in the various 

 groups. The observed results were 27, 48, 

 87, 42, 16, respectively, giving a ratio of 

 1.98 : 3.47 : 6.33 : 3.05 : 1.16. The agree- 

 ment on the whole is remarkably close con- 

 sidering the difficulty of classifying some of 

 the tip-awned plants. The only serious 

 divergence is in the bald class where the de- 

 viation is over five times the probable error. 

 A deviation of five times the probable error 

 stands a 1310 : 1 chance of being signifi- 

 cant. Possibly this deviation is due largely 

 to the difficulty of correctly distinguishing 

 between bald and almost bald spikes, result- 

 ing in too many individuals being placed in 

 the bald class. The Howards (9) drew at- 

 tention to the liability of such an error. It 

 will be noticed that' the BBtt, bbTT and 

 BbTt genotypes are placed in one class in 

 the table. It is frequently possible to sep- 

 arate these into three classes on phenotypic 

 appearance (6 and 9) but it was not thought 

 advisable here. 



The factor grouping for presence or ab- 

 sence of awns in the parent varieties and in 

 the Fo material may be summarized as fol- 

 lows : 



