68 



IRISH GARDENING 



the kind of hybrid will be produced and the 

 progeny again M'ill be the same A\'hether the 

 hybrid was prodiiced in one way or the other. 



(3) .4^ to the remaining characters in which 

 the parents do not differ. — We do not know 

 whether Mendel's peas were absolutely alike in 

 all other characters than those in which he 

 observed them to differ. Probably they were 

 not and he neglected the remainder as un- 

 essential to the main issue. This can be said, 

 however, that, if the hybrids between two 

 parents have two kinds or four kinds or eight 

 kinds or any other 2)ossible number of kinds of 

 progeny, then their 2)arents differed in one, two, 

 three or more pairs of characters, as the case 

 may be, but the remaining characters in each were 

 the same. This princijile can be used for com- 

 paring plants which have not been mated. 

 For instance, if j^lant A differs from B as regards 

 X and X only, then their remaining characters 

 may be written dov.n : — 



A = XYZPQR . . . 

 B = xYZPQR . . . 



If B differs from C as regards Y and y, then 

 their remaining characters may be written 

 dowai : — 



B = xYZPQR . . . 

 C = xyZPQR . . . 



If C differs from D as regards Z and z, their 

 remaining characters may be written down : — 



C = xyZPQR . . . 

 D = xyzPQR . . . 



(4) As to ivhere to look jor information. — 

 Frequently it is possible to gain much informa- 

 tion from the hjd^rids themselves. The hybrids 

 show all the dominant characters, and the 

 characters which disappear are their recessives. 

 If there be any doubt as to which dominant and 

 which recessive make a pair, the doubt can be 

 settled by the next generation. For instance, 

 in the two pair set of four groups — 



X X X x 



Y V Y V 



9:3:3:1 



Each of the two groujis of three — the two 

 middle groups — shows one dominant and the 

 recessive of the other. 



If we look back to section {d) we see that each 

 group of nine in the three-j^air set of eight 

 groups carries two dominants and the recessive 

 of the third, while each grouj:) of three carries 

 two recessives and the dominant of the third. 



(5) If the progeny of hyl)rids have been 

 separated into 4, 8, 16 or more groujis, any j)air 

 of characters may be neglected Avithoiit the 

 distribution of the remaining characters being 

 interfered with. For instance, when Mendel 



nuited peas differing in three pairs of characters 

 he found the hybrids" jirogeny to be as follows : — 



Round, yfll'JW alhuim-n, coloured .-ccd-coat 2(i9 i.e. 27 



Round, yellow „ white „ U8 !» 



Round, green ,, coloured „ 86 il 



Wrinkled, yellow ,, coloured ,, 88 it 



Round, i^reen ,, white ,, 27 'i 



Wrinkled, yellow ,, white ,, 34 '.i 



Wrinkled, green ,, colouied „ 30 :} 



Wrinkled, green ,, white ,, 7 1 



If the last pair of characters be neglected, 

 the three-pair set of eight groups becomes a 

 two-pair set of four groups, thus : — ■ 



Round, yellow 3(57 i.e. i) 



Round, green 113 3 



Wrinkled, yellow 122 3 



Wrinkled, green 37 1 



If either of these pairs be neglected, then the 

 two-pair set of four groups becomes a one-pair 

 set of two groujas, thus : — 



Round 480 i.e. 3 

 Wrinkled 159 1 



(6) If the original jDarents differ in any number 

 of pairs of characters, and the members of each 

 pair are related to each other by ordinary 

 dominance and recessiveness, then, if sufficient 

 second generation progeny are bred, the usual 

 number of types must be produced, but, if one 

 or more types be inseparable by the eye, the 

 number of observable groups will be one less than 

 the normal for every type that is inseparable 

 from another and the numbers in one group will 

 be the sum of the numbers in the two inseparable 

 types together. If, for instance, the first two 

 of four types be inseparable there will be three 

 groujis in the ratio 12 : 3 : 1, thus : — 



X X X X 



Y V Y v 

 9 : 3 : 3 : 1 



12 : 3 : 1 



If the last two tyj)es be inseparable, there will 

 be four groups in the ratio 9 : 4, thus : — 



X X X X 



Y y Y v 

 9 : 3 : 3 : 1 



9:3: 4 



If the last three types be inseparable, there 

 Avill be two groujjs in the ratio 9:7, thus : — 



X X X X 



Y y Y v 

 9 : 3 : 3 : 1 



9 : 7 



There are others, to which A\e may return 

 again. Next month we shall consider the 

 apiDlication of the theory to some of the 

 irregular problems which have arisen. 



