Ij, Ig, I3. — First, second and third generations of self-fertili- 

 zation. 

 larovization. — Vernalization, q.v. 

 Id. — Weismann's term for a hereditary unit "necessary to the 



production of a complete individual". 

 Idant. — An obsolete synonym for chromosome, q.v. 

 Identical Twins. — Monozygotic twins, i.e. both originating 



from the one fertilized ovum. 

 Idio-adaptation. — Evolutionary changes which bring about 



specialization and a progressive restriction of the mode of life 



of the organism. 

 Idiochromatin. — Nuclear chromatin controlling cell division 



but otherwise dormant. 

 Idiochromidia. — Chromidia having a reproductive function 



and derived from idiochromatin. 

 Idiochromosome. — A sex chromosome; a chromosome which 



has no truly similar homologue in the heterozygous sex. See 



also under W-, X- and Y-chromosomes. 

 Idiogram. — A diagrammatic representation of the chromosome 



complement of a karyotype. 

 Idioplasm. — The generative portion of a cell as distinct from 



the vegetative, or nutritive, portion. Nageli's term for the 



hereditary substance passed on from one generation to another ; 



germplasm ; chromatin. 

 Idiosome. — Idiozome, q.v. 

 Idiotype. — The individual genotype. 

 Idiovariation. — A mutation. 

 Idiozome. — The zone of non-granular protoplasm around 



the centrosome; the attraction sphere. 

 Illegitimate Pollination. — Artificial self-pollination of a 



flower which is specialized for cross-pollination. 

 Imaginal Tissue. — Undifferentiated tissue in the larva or 



embryo from which the external organs of the final instar 



(the imago or fully adult insect) develop. Specifically such 



tissues are called Imaginal buds, discs, disks. 



