Knight — 150 — Dictionary 



Transgenation. — A heritable change taking place at a single 



gene locus, presumably caused by chemical alteration of the 



individual gene; a mutation proper, point-mutation or geno- 



variation. 

 Transgressive Segregation. — The appearance in the Fg (or 



later) generation of a cross of individuals showing a more 



extreme development of a character than either parent (J. 



Heredity). 

 Transient Polymorphism. — See under Polymorphism. 

 Translocation. — The shifting of a segment of a chromosome 



to another part of the same chromosome, or the attachment of 



a fragment of one chromosome to a non-homologous chromo- 

 some. 

 Traumatin. — Cj^H^^O^N; a plant wound-hormone which 



stimulates cell division, cf. Allantoin. 

 Triad. — Three daughter cells arising (instead of a tetrad) 



from a spore mother-cell, as a result of meiotic irregularities. 

 Triaster. — Used of cell division when a spindle mechanism 



is formed having three poles. 

 Tribe. — A combination of one or more families, the foundresses 



of which trace in the female line to a common ancestress which 



is the foundress of the tribe (Winters). 

 Trichlamydeous. — Of a perclinal chimaera {q.v.) : having the 



genetically distinct peripheral tissue three layers of cells thick. 

 Trigamous. — Having pistillate, perfect and staminate flowers 



all present in the one head. 

 Trigeneric Hybrid. — An individual produced by crossing 



two distinct genera and crossing the F^ with a third genus. 

 Trigenic. — Controlled by three genes. 

 Trigynous. — Three styled. 



Triheterozygote. — An organism heterozygous for three genes. 

 Trihybrid. — A hybrid resulting from a cross between parents 



differing in three genes. 

 Trimonoecious. — Having perfect, staminate and pistillate 



flowers on the one plant. 

 Trimorphism. — The occurrence of three distinct forms within 



a species. See Polymorphism. 

 Trioecious. — Having perfect, staminate and pistillate flowers 



on different individual plants within the species. 

 Triphenyl Chloro-ethylene. — See under Oestrogens. 

 Triple Fusion. — The fusion between the two polar nuclei and 



a male gamete, which takes place in the embryo-sac and which 



gives rise to the endosperm. 



