Ii, Li It — 79 — Indole-S-acetic Acid 



Immunity. — Complete resistance to any particular disease or 

 pest. 



Imperfect Arrhenogenic. — An individual which produces 

 broods in which males predominate, only a small proportion of 

 females being present. 



Imperfect Flower. — One which is not functionally (or ana- 

 tomically) hermaphroditic. 



Implant. — A grafted portion of tissue. 



Impregnation. — The deposition of spermatozoa within the 

 body of the female whether brought about by coitus or arti- 

 ficially; insemination. 



Inantherate. — Lacking anthers. 



Inarching. — The grafting of a branch of one plant onto 

 another plant without cutting the branch away from the parent 

 plant until union is complete. 



Inbred Line. — A line showing a considerable degree of homo- 

 zygosity as a result of continued inbreeding and selection. 



Inbred-variety Cross. — The F^ produced by crossing an 

 inbred line and a commercial variety. 



Inbreeding. — Breeding between close relatives, especially 

 when repeated for several generations; endogamy. 



Inbreeding Coefficient. — See Appendix 1. 



Incasement. — Preformation. See under Epigenesis. 



Incompatibility. — The inability of pollen to bring about 

 fertilization because the pollen-tubes are arrested in the style 

 and prevented from reaching the ovules. 



Incomplete Penetrance. — Said of a gene which, though 

 normally dominant or partially dominant, sometimes fails to 

 produce an effect on a heterozygote, also of a recessive gene 

 which does not always have any effect in the homozygous 

 state. See also Penetrance and Complete Penetrance. 



Independent Assortment. — The segregation of genes in 

 gamete formation without any particular genes occurring to- 

 gether more frequently than would be expected on a chance 

 basis. 



Independent Characters. — Characters governed by genes 

 showing independent assortment, q.v. 



Independent Genes. — Genes which show independent as- 

 sortment, q.v. 



Index-breeding. — A system of breeding in which the value 

 of each sire is computed as a numerical 'index' from the rela- 

 tion of daughter's productive ability to that of their dams. 



Indole-3-acetic Acid. — A plant growth hormone which has 

 been used successfully in inducing polyploidy. 



