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On-Line Glossary: V

Each entry consists of a term (in bold), a definition of the term, and a number in parentheses (0) indicating the source of the definition. Clicking on the speaker icon will give you the pronunciation of the term. (Be sure to close the window for the sound player after each use.) The pencil icon will give you a drawing, and the camera icon will give you a photograph.


vagina. In nematodes: A canal, lined with cuticle, that connects the uterus or uteri with the female gonospore. (14)

valid. Of taxonomic names and epithets: Published in accordance with several articles of the Code of Nomenclature; such names may be legitimate or illegitimate. (22)

valve. In nematodes: A structure that regulates the rate and/or direction of intake of materials (e.g., the esophago-intestinal valve or cardia). (14)

valvulated. Having small valves. (18)

var.. Variety. (21)

variety. In fungi: A rank below subspecies. (16) In bacteria: Formerly a rank equivalent to subspecies; currently an infrasubspecific rank which has no official standing in nomenclature. (16)

vas deferens. In nematodes: A slender, tube-like gonoduct in the male; unites posteriorly with the rectum to form the cloaca. (14)

vector. An living agent that transmits a pathogen from an infected plant to an uninfected one. (3)

vegetative. A cell or structure that is not producing reproductive structures, usually in the assimilative state. (15)

vegetative reproduction. Asexual reproduction. (20)

vein banding. A symptom of virus-infected leaves in which tissues along the veins are darker green than other laminar tissue. (20)

vein clearing. A symptom of virus-infected leaves in which veinal tissue is lighter green than that of healthy plants. (20)

ventral. Front, or lower surface. (7)

vermicular. Worm-shaped, thickened and bent in places. (Also vermiculate.) (17)

vermiculate. See vermicular.

vermiform. Worm-like. (7)

verrucose. Having small, rounded processes or "warts". (7)

vertical resistance. In a given cultivar: the existence of differential levels of resistance to different races of a given pathogen. (3)

vesicle. A bladder-like sac or an evanescent bubble within which zoospores mature; any bubble-like cell or bubble-like membranous structure within a cell. (15)

vessel. A xylem element or series of such elements whose function is to conduct water and mineral nutrients. (2)

vestigial. Pertaining to structures or organs that were well developed in an organism's ancestors but have become rudimentary during the course of evolution. (14)

viable. Living, able to germinate or grow. (17)

virescence. Greening of tissue that is normally devoid of chlorophyll; the abnormal development of flowers in which all organs are green and partly or wholly transformed into structures like small leaves. (8)

virescent. A normally white or colored tissue that develops chloroplasts and becomes green. (2)

virion. The infectious unit of a virus. (10)

viroid. Any of numerous kinds of small particles (250-400 nucleotides) of circular, single-stranded RNA that is unencapsidated and encodes no known proteins. (5)

virulence. The degree of pathogenicity of a given pathogen. (2)

virulent. Capable of causing a severe disease; strongly pathogenic. (2)

viruliferous. Used to describe a vector containing a virus and capable of transmitting it. (10)

virus. Infectious units comprising either RNA or DNA enclosed in a protective coat. (2)

viviparous. Bearing living young. (14)

volva. A cup-like structure at the base of a basidiocarp (in the Basidiomycetes). (15)

volvate. Having a volva. (17)

vulva. In nematodes: Exterior opening of the mature female's reproductive system (female gonopore); generally appears as a transverse slit on the ventral portion of the nematode. (14)

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