Knight — 136 — Dictionary 



Short-day Plants. — Plants in which the commencement of 

 flowering is speeded-up by a reduced period of dayUght (nor- 

 mally less than twelve hours). Opp. Long-day Plants. 



Sibbing. — Intercrossing brothers and sisters. 



Sibling, Sib. — One of two or more children of the same 

 parents but not, necessarily, of the same birth. 



Sibling Species. — Sympatric forms which are morphologically 

 very similar or indistinguishable, but which possess specific 

 biological characteristics and are reproductively isolated 

 (Mayr, 1942). 



Sibmating. — The crossing together of individuals of the 

 same immediate parentage, i.e. the mating of brothers with 

 sisters. 



Silent Heat. — An oestrus cycle in which ovulation occurs 

 but in which the outward signs of heat are lacking. 



Silks. — The styles and stigmas in maize. 



Simple Polyembryony. — Polyembryony brought about as 

 a result of the formation of several eggs from a single mega- 

 spore. 



Simplex. — (i) Heterozygous for a particular dominant gene, 

 (ii) Of a tetraploid: having only one dose of a particular 

 dominant gene (Aaaa). 



Simplex-insufficient. — Used of duplicate genes to indicate 

 that neither of them will, in the heterozygous state, give full 

 expression to the character. 



Simplex-sufficient. — Used of duplicate genes to indicate 

 that either of them, in the heterozygous state, gives full ex- 

 pression to the character. 



Single-dose Expression. — The degree of dominance or lack 

 of dominance shown by a gene in the heterozygous state. 

 Full single-dose expression is the equivalent of full dominance 

 (true dominance), partial single-dose expression is partial 

 dominance and absence of single-dose expression is the same 

 as complete recessiveness. 



Siphonogamy. — Fertilization when carried out by pollen 

 tube. 



Skein. — Spireme, q.v. 



Slip. — A shoot, from the collar or lower part of the stem of 

 a plant, used for propagation. 



S-M-C. — (i) Spermatocyte, or sperm mother-cell. See under 

 Spermatogonium, (ii) Spore mother-cell, q.v. 



Sobole. — A rhizome or underground creeping stem. 



