Structural Hybrid — 143 — Synantherous 



Superspecies. — A monophyletic group of geographically 

 representative (allopatric) species which are morphologically 

 too distinct to be included in one species (Mayr, 19^2). 



Supplementary Factors. — Factors which by themselves have 

 no effect but which qualitatively alter the effect of another 

 factor; modifying factors. 



Suppressor. — Any gene which, either in the heterozygous 

 or homozygous state, nullifies the effect of a major gene but 

 which, by itself, has no effect. 



Suppressor Mutation. — A sudden change occurring at a 

 particular chromosomal locus such that a gene is formed cap- 

 able of nullifying the effect of a particular major gene. 



Surculigerous. — Reproducing by suckers. 



Surculose. — Producing suckers which give rise to independent 

 plants. 



Surculus. — A sucker. 



Survival of the Fittest. — The corollary of the theory of 

 Natural Selection namely that, as a result of the elimination 

 by natural selection of those individuals least suited to the 

 environment, those which ultimately remain are the fittest. 



Switch Genes. — Genes which cause certain regions of de- 

 veloping tissue to take an abnormal choice out of a range of 

 alternative possible paths (Waddington). 



Symmetrical Chiasmata. — Chiasmata which are either reci- 

 procal (q.v.) or complementary (q.v.) ; comparate chiasmata. 

 0pp. Disparate Chiasmata. 



Sympatric. — Inhabiting one and the same area. 



Sympatric Hybridization. — The production of a hybrid be- 

 tween two good species that coexist over wide parts of their 

 ranges without mixing (Mayr, 1942). 



Sympatric Speciation. — Reproductive isolation and specia- 

 tion which takes place within a single local population. This 

 can occur either instantaneously (q.v.) or by ecological spe- 

 cialization (cf. Mayr, 1942). 



Sympatric Speciation, Instantaneous. — The production of 

 a single individual (or the offspring of a single mating) which 

 is reproductively isolated from the species to which the parental 

 stock belongs (Mayr, 1942). 



Sympetalous. — With petals united to form a tube; gamo- 

 petalous. 



Symplast. — Coenocyte, q.v. 



Synacme. — The simultaneous maturation of pollen and stig- 

 mas. 



Synantherous. — With anthers joined to form a tube. 



