836 Appendix 



Histogenesis (his to -jen' e sis) (Gr. histos, web, tissue; gen, to form), tissue for- 

 mation and development. 



Histology (his-tol'oji) (Gr. histos, web, tissue; logos, study), study of tissues 

 and cells. 



Holophytic (hoi o -fit' ik) (Gr. holos, whole; phyton, plant), plants that manu- 

 facture their own food (contrast with Holozoic). 



Holozoic (holo-zo'ik) (Gr. holos, whole; zoon, animal), securing nourishment, 

 as in animals, by ingesting and digesting organic materials (contrast with 

 Holophytic). 



Homologous chromosomes (ho -mol' o gus) (Gr. homos, same; logos, speech), a 

 pair of chromosomes, one from each parent, that have relatively similar 

 structure and gene values. 



Homologous genes, genes similarly located in homologous chromosomes, con- 

 tributing to the same expression or a different expression of a trait. 



Homology (ho-mol'oji) (Gr. homos, same; logos, study), parts or organs which 

 are similar structurally and which have originated embryologically in a 

 similar way; for example, the forelegs of a dog and frog show homology. 



Homonomous segmentation (ho -mon' o mus) (Gr. homos, similar), similar seg- 

 ments (metameres) as in the earthworm (contrast with Heteronomous). 



Homoptera (ho -mop' tur a) (Gr. homos, same; ptera, wings), order of insects 

 whose wings are similar and membranous throughout (contrast with 

 Hemiptera). 



Homospory (ho -mos' po ri) (Gr. homo, same; spora, spore), production of like 

 spores (contrast with Heterospory). 



Homozygote (ho mo -zi' got) (Gr. homo, same; zygon, yoke), union of gametes 

 that are alike in their gene content (contrast with Heterozygote) . 



Hormogonia (hor mo -go' ni a) (Gr. hormos, chain; gonos, offspring), portions of 

 algal filaments able to form new individuals. 



Hormone (hor' mon) (Gr. hormaein, to excite), a chemical substance secreted by 

 one organ and producing a specific effect in another. 



Host (L. hostis, stranger), an organism in or on which a parasite lives. 



Humerus (hu'merus) (L. humerus, shoulder), upper arm bone. 



Hyaline (hi'alin) (L. hyalos, glass), clear or transparent as hyaline cartilage. 



Hybrid (hi'brid) (L. hybrida, mongrel), a crossbred animal or plant; the off- 

 spring of two parents who differ in at least one trait. 



Hydrogen-ion concentration (pH), the index of acidity due to the number of 

 positive hydrogen ions concentrated in a solution. 



Hydroid (hi'droid) (Gr. hydra, water; cidos, like), resembling Hydra. , 



Hydrolysis (hi -drol' i sis) (Gr. hydor, water; lysis, destroy), destruction of a 

 chemical substance by the addition of the elements of water. 



Hydroponics (hi dro -pon' iks) (Gr. hydro, water; ponus, exertion), growth of 

 plants in liquid culture media (soilless cultivation). 



Hydrostatic (hi -dro -stat' ik) (Gr. hydor, water; L. statique, weigh), regulating 

 the specific gravity of an organism in relation to that of water, as the 

 air bladder of certain fish. 



Hydrotropism (hi -drot' ro pizm) (Gr. hydor, water; trope, turning), response of 

 organisms to water. 



Hydroxyl (hi -drox' il), the radical OH. 



