Hereditary Univalents — 69 — Heterogenesis 



Heterochromatism. — Appearance of different colours in the 

 flowers of the same infloresence due to seasonal differences 

 (Carpenter). 



Heterochromaty. — Differential staining. 



Heterochromosomes. — Chromosomes distinguished by special 

 peculiarities of behaviour, form, or size in contradistinction 

 to autosomes or euchromosomes (Montgomery; Wilson). 



Heterochrony. — A reversal in the sequence of developmental 

 stages during evolution. 



Heteroclinous. — Heterocephalous, q.v. 



Heterofertilization. — The process responsible for the pro- 

 duction of seed in which embryo and endosperm differ gene- 

 tically, generally as a result of 'fertilization' by two unlike 

 pollen grains, the sperm from one of which fertilizes the G^gg 

 cell whilst the generative nucleus of the other unites with the 

 two polar nuclei. 



Heterogameon. — A species made up of races which, if selfed, 

 produce morphologically stable populations, but when crossed 

 may produce several types of viable and fertile offspring 

 (Camp & Gilly). 



Heterogamete. — A gamete differing in its properties of sex 

 determination, or morphologically, from the other conjugant; 

 anisogamete. 



Heterogametic. — Producing gametes of more than one kind, 

 which differ in regard to their properties of sex determination 

 or in the chromosomes which they contain. Opp. Homogame- 

 tic. 



Heterogametic Sex. — The sex which has two dissimilar sex 

 chromosomes in its body cells {e.g. the human male). 



Heterogamety. — The production of gametes having different 

 properties of sex determination. 



Heterogamous. — (i) Bearing two or more kinds of flowers 

 on the one inflorescence, often a unisexual peripheral group 

 and a perfect central group as in Compositae. (ii) Hetero- 

 gametic, q.v. 



Heterogamy. — The condition of having gametes which are 

 dissimilar especially in regard to their properties of sex de- 

 termination. 



Heterogenesis. — (i) Alternation of generations; an alterna- 

 tion of a sexual with an asexual form or, cytologically, the 

 alternation of a haploid with a diploid stage, (ii) The appear- 

 ance of a new distinct form differing from its parents and 



