Qualitative Characters - The characters of community studied by subjective assessment and may be grouped in point scales. For plant communities examples of such characters are physiognomy, phenology, stratifiction, sociability, vitality, life forms; interspecific association, floristics etc.

Qualitative Variation (discontinuous variation). The expression of a characteristic perceptibly different ways by different individual of a population. Such variation may be attributed to either recurrent mutation or to the existance of a balanced polymorphism. Mendelian characteristics are examples of qualitative variation.

Quantitative Inheritance - The inheritance of characters in which the variation is continuous.

Quantitative Variation (continuous variation). The type of variation shown by a characteristic which is exhibited by all the members of a population to a greater or lesser extent. An example is the size of ears in a cereal crop. Such characters have been found to be strongly influenced by environment and are determined by many genes each with a small effect.

Quaternary - The second period of Cenozoic era from about two million years ago to present day. ,It has been divided into Pleistocene and Holocene epochs. At its start, climate was cool and temperate and during it there were four glacial ages. Many plant and animal species become extinct during this period. In the present Holocene epoch, crop plants and their associated weeds had been originated with rise of human civilization.

Quercitin - A flavonal which is found in the free state or combined in glycosidal forms in a wide range of flowers, leaves etc.

Quiescent Centre - The region in apical meristem of a root in which little or no cell division takes place. Cells of the region could undergomeristematic activity if meristem initials are damaged thereby acting as reservoir of potential initials and are protected from damage by their relative inactivity. The centre may also be used as site of auxin synthesis.