Rg Generation. — The progeny obtained by crossing a hybrid 

 with one of its parents; a backcross progeny. 



Rassenkreis. — Rheogameon, q.v. 



Rate-gene. — A gene controlling the speed of any particular 

 developmental process. 



Ratios. — See under Backcross Ratios, Fg Ratios, Progeny Size 

 and Appendix 1. 



Ratoon. — A shoot from the base of the stem, or from the 

 root, of a plant which has been cut back. 



Ray Floret. — One of the peripheral, typically uni-sexual, 

 strap-like flowers arranged radially in a capitulum or other 

 compact inflorescence. 



Recapitulation. — The theory that the developmental stages 

 of the individual's life-history recapitulate, in summarized 

 form, the evolutionary life-history of the race; that is that 

 ontogeny recapitulates phylogeny. 



Receptive. — Of a stigma; ripe for germinating pollen. 



Recessive Character. — That one, of a pair of allelomorphic 

 characters which will not appear when both allelic genes are 

 present. 



Reciprocal Chiasmata. — Chiasmata formed between two 

 chromatids in such a way that a double crossing-over occurs 

 in which the other two chromatids are not involved. 



Reciprocal Cross. — A second cross involving the same char- 

 acters as the first but with the sexes of the parents interchanged. 



Reciprocal Translocation. — Mutual translocation; a cross- 

 ing over between non-homologous chromosomes. 



Recombination. — The rearrangement of linked genes due to 

 crossing-over. 



Recombination Fraction. — The gametic output in a hybrid 

 of new combinations of two genes expressed as a fraction or 

 percentage of the total gametic output of new and old com- 

 binations combined. The formulae for the gametic output 

 of the double heterozygote AaBb are (i) Coupling: ^(1 - 

 p)AB, 54pAb, i^paB, ^(1 - p)ab; (ii) Repulsion: 5/2PAB, 



