576 APPENDIX 111 



phase of the life-cycle, particularly in the Basidiomycetes where nuclear 

 fusion does not immediately follow cell-fusion. Goebel. 



Diplotene, the stage of meiosis which follows division of the chromosomes at 

 the pachytene stage, v. Winiwarter, 1900. 



Disjunction, the separation of chromosomes at anaphase, particularly of the 

 first meiotic division. 



Dislocated segments, homologous pairs of segments in a different linear 

 sequence from other segments in a structural hybrid. 



[Dislocation], structural change. Navashin, 1926, 1932. 



Distal, that part of a chromosome which relative to another part is further 

 from the centromere. 



Duplication. The occurrence of a segment twice in the same chromosome, 

 or in the same complement or the change by which this condition arises. 

 Bridges, 191 7. 



Dyad, (i) the pair of cells formed after meiosis through irregularity instead of 

 a quadruple " tetrad " {q.v.) ; [(ii)] the univalent chromosome, composed 

 of two chromatids, at meiosis. 



Embryo-sac, the female gametophyte in the angiosperms. 



Environment, those factors external or antecedent to an organism which are 

 related to its development. Its reaction with the genotype determines 

 the phenotype. N.B. — Dissimilar genotypes themselves imply dis- 

 similar environments. 



[Ergastic], of materials in the cell : the non-living products of metabolism 

 {e.g., many fats and carbohydrates). A. Meyer, 1896. 



Factor, the hypothetical determinant of a character in respect of which an 

 organism may show a mendelian difference. It is usually an abstract 

 description of a gene difference. Bateson and Punveit, 1905. 



Fertilisation, the fusion of two germ-cells and of their nuclei, without which 

 their later development is usually impossible. 



First Division, the first of the two meiotic divisions, formerly known as the 

 " heterotypic " or " reduction " division. 



Gametes, germ cells which are specialised for fertilisation and cannot normally 

 develop without it. 



Gametophyte, the haploid plant which produces the gametes where there is an 

 alternation of generations. 



Gene, the unit of reproduction and hence of crossing-over in the hereditary 

 material. Johannsen, 191 1, 1923 ; Morgan, 1925. Its change may be 

 inter-genic and structural, or intra-genic and molecular. D., 1932. 



Genetic, of a property possessed by an organism by virtue of heredity. Bate- 

 son, 1906. 



[Genome], a chromosome set, q.v. Winkler., 1916. 



Genotype, the kind or type of the hereditary properties of an individual 

 organism. Johannsen, 191 1. 



Genotypic Control, the control of chromosome behaviour by the hereditary 

 properties of the organism. D., 1932 a. 



Golgi apparatus, bodies in the cytoplasm, so-called in anticipation of their 

 proving to be an apparatus. 



Haploid {v. Diploid). Strasburger, 1905. 



" True ," an organism having one set of chromosomes (v. Text). 



Haplo-diploid Sex Differentiation, that in which the sexes are distinguished 

 by the male being haploid, the female diploid {v. Text). 



Heredity, the process by which like begets like (in sexual reproduction). 1863. 



[Heterochromosomes], chromosomes of exceptional form or behaviour, 

 especially at meiosis, such as sex chromosomes, fragments, etc. Mont- 

 gomery, 1904. 



