Palingeny — 111 — Passive Adaptation 



Paraplasm. — Passive cell material. 



Parastamen, Parastemon. — A sterile stamen. 



Parasynapsis. — The side-by-side conjugation of chromosomes 

 at the zygotene stage of meiosis. 



Parasyndesis. — Parasynapsis, q.v. 



Para variation. — A modification or acquired variation de- 

 veloped during the life of the individual as a result of en- 

 vironmental causes and not heritable. 



Paripotency. — Similarity of basic evolutionary potentiality 

 between different species. 



Parthenapogamy. — The conjugation or fusion of tv^^o somatic 

 nuclei. 



Parthenocarpy. — The formation of fruit without fertilization 

 and without seeds, or with embryo-less seeds. 



Parthenogamy. — Fusion of two female gametes. 



Parthenogenesis. — {See also under Reproduction). The 

 development of an organism from a female or a male gamete 

 without fertilization. There are two types: 

 (i) Diploid Parthenogenesis, in which the reduction divi- 

 sion of meiosis is abortive so that diploid ova are formed which, 

 later, may develop without fertilization. 



(ii) Haploid Parthenogenesis, in which normal ova with 

 the gametic chromosome number develop without fertilization. 

 Individuals produced by haploid parthenogenesis may have 

 n or 2n chromosomes in their body-cells according to whether 

 the unfertilized ovum does or does not double its chromosome 

 number as the first step in development. 



Parthenosperm. — A sperm capable of developing as a zygote 

 without having fused with a female gamete. 



Parthenote. — A haploid individual arising parthenogenetically. 



Partial Dominance. — A reduced dominance characterized by 

 the production of an intermediate phenotype in individuals 

 heterozygous for the gene concerned; semi-dominance. 



Partial Sex Linkage. — This occurs when the gene concerned 

 is located on the homologous region of the X- or Y-chromosome 

 so that crossing-over between the X- and Y-chromosomes can 

 transfer the gene from one to the other. 



Particulate Inheritance. — That in which distinctive charac- 

 ters from both parents appear in their offspring; mendelian 

 inheritance. 



Parturition. — The process of giving birth in viviparous ani- 

 mals. 



Passive Adaptation. — Pre-adaptation, q.v. 



