Tropisms

The response of plants to stimuli, resulting in growth taking place being towards or away from the stimuli. The main tropisms are Phototropism; Gravitropism; and Thigmotropism.

  Uneven Cut

An uneven cut which will typically produce a ridged type of appearance, with one side of the mower being set to a different height than the other side.

  Uniformity

Plant Breeders have rights of protection over plant varieties with uniformity being assessed for all characteristics used to establish Distinctness and 'A variety can be considered sufficiently uniform after two years of tests'.

  Vacuole

A container, called a sac, within a plant cell which contains fluids which can expand the sac up to about 90% of the cell volume, when well supplied with water, producing more turgid plant cells. When water is in limited supply, especially during drought conditions, then vacuoles will contract creating flaccid plant cells.

  Variance

The average of the squared deviation (or difference) of a variable from the mean; this identifies the extent of the dispersion or spread of the values. The variance is helpful for making inferences from data, although standard deviation (which is the square root of the variance) is often the preferred method of determining variability in data. Two methods of variance are used, either population variance (where all data of a group are included – this would only be applicable for small surveys) or sample variance (where a sample of a group is being used and is probably the most common approach).

  Variety

A plant taxonomic category between a species and a form. A variety is a naturally occurring organism without human intervention, unlike a cultivar, and it exhibits a minor difference within a species (or sub-species). This is a plant with a minor variation from the main species description, for example, a plant with variegated leaves.

  Vegetation Reproduction

The continued establishment and reproduction of a plant without being reproduced from seed. Grasses vegetatively reproduce due to growth by stolons, rhizomes and tillering. Vegetative reproduction is a common type of asexual reproduction in grasses, especially turfgrasses.

  Vernalisation

The process in which plants are exposed to cold conditions to encourage them to initiate flowering. The extent of exposure can vary from a few weeks to several months, and from temperatures at zero Celsius or higher. Vernalisation helps plants ensure they do not flower too early, which increases their chances of survival and reproduction. Winter wheat is a typical example of an annual plant that germinates in the autumn, and seeds in late spring to early summer.

  Vertebrate

An animal with a backbone (i.e. a vertebrae). Mammals, birds, reptiles and amphibians all fall within this category.

  Vesicular-Arbuscular Mycorrhiza

A symbiotic association between a fungus (from the phylum Glomeromycota) and plant roots. Also called Endomycorrhiza, see Mycorrhizae.