(_a_) Purple (_a_) Painted Lady (_b_) Deep Purple (_b_) Miss Hunt (_c_) Picotee (_c_) Tinged White The varied forms in the F_2 generation appear in definite proportions and a certain number of plants of each variety are already "fixed," and have been shewn, by further experiment, to breed true to type. [Sidenote: M 5] Experiment with Sweet Peas, illustrating reversion in structural characters. A cross between the ordinary "Cupid" dwarfs and the half-dwarf "Bush" form results in a complete reversion to the normal tall habit such as occurs in the wild sweet pea. A further generation raised from these reversionary talls consists of talls, Bush, Cupids, and a new form, the "Bush-Cupid." These last combine the erect bush-like habit of growth with the dwarfness of the Cupid. Bush × Cupid | F_1 Tall | +----------+----+----+------------+ | | | | F_2 Tall Bush Cupid Bush-Cupid In the ratio 9 3 3 1 [Sidenote: M 6a] Example of +association of characters in heredity+. In the sweet pea the dark reddish purple axil is dominant to the light green one. Also the fertile condition of the anthers is dominant to the contabescent sterile condition. In families which involve these characters, the nature of the F_2 generation depends upon the way in which the original cross was made. (A) When each parent has one of the dominant characters. Dark axil} {Light axil Sterile} × {Fertile | F_{1} Dark axil Fertile | +------------+---+---------+----------------+ | | | | F_{2} Dark axil Dark axil Light axil {[*]Light axil} Fertile Sterile Fertile { Sterile } Approximate 2 1 1 ratio * Not yet found, but probably occurs very rarely.] [Sidenote: M 6b] (B) If, however, both of the dominant characters go in with one parent, and neither with the other parent, they tend to remain associated in F_{2}; thus:-- Light} {Dark Sterile} × {Fertile | F_{1} Dark Fertile | +-----------+----------+-----------+ | | | | F_{2} Dark Dark Light Light Fertile Sterile Fertile Sterile +Ratio.+ 737 31 31 225