Dialycarpie — 41 — Dihaploid 



Dictyotic Stage. — The period when the chromosomes are 

 transformed into the nuclear reticulum. 



Didiploid. — An autotetraploid, autopolyploid or duplicational 

 polyploid; a tetraploid whose somatic nuclei contain four 

 similar sets of chromosomes. 



Didynamous. — Having only four stamens of which two are 

 short and two are long. 



Dienoestrol. — A synthetic oestrogenic hormone more power- 

 ful than the natural product. 



Dientomophily. — The state of having some members of the 

 species adapted for pollination by one species of insect whilst 

 others are pollinated by a different species. 



Differential Affinity. — The differential attraction which exists 

 between chromosomes showing residual homology as com- 

 pared with truly homologous chromosomes, so that though 

 two chromosomes with residual homology can pair, they will 

 not do so in the presence of the true homologue of either of 

 them. 



Differential and Interference Distances. — These are, re- 

 spectively, the distance between the centromere and the mean 

 position of the proximal chiasma, and the mean distance be- 

 tween the proximal or first and the next proximal or second 

 chiasma (Mather, 1940). 



Differential Precocity. — See under Precocity. 



Differential Segment. — A segment of a chromosome which 

 has no exact equivalent in the other member of the bivalent. 

 0pp. Pairing Segment. 



Differentiation. — The specialization of cells and tissues which 

 takes place during the growth of an embryo and which even- 

 tually enables the various tissues to function as the specialized 

 organs which make up the adult organism. 



Digametic. — Having gametes of two classes, male and female. 

 N. Digamy. 



Digenesis. — Alternation of generations; an alternation of a 

 sexual with an asexual form, or, cytologically, the alternation 

 of a haploid with a diploid stage. 



Digeneutic. — Having two breeding seasons per year. 



Digenic. — Controlled by two genes. 



Digenomic Species. — A species whose gametes all carry 

 two sets of chromosomes, i.e. a tetraploid species. 



Digynous. — With two carpels. 



Dihaploid. — An individual derived from a tetraploid but 

 carrying only half the normal tetraploid chromosome comple- 

 ment. 



