Adventitious: Developing from unusual points of origin, such as shoots or roots arising from a leaf or stem tissues other than the axils or apex; and embryos from any cell other than the zygote.

Determined: Cells that are committed to a particular pathway of development or differentiation but which have yet to overtly express this pathway.

Heterotrophic: Dependent on an external energy source; not self-reliant compare to autotrophic.

Ploidy: Term used to describe the number of genomes present in the nucleus of a cell or plant.

Polarity: In plants, like in animals, the axes appear very early in development and mostly they are polar in nature. The gradation or change in character occurs along the axis from one end to the other and the condition is referred as ‘polarity'. It is visible as morphological differentiation during the development of shoots and roots or is invisible, physiological effect which is expressed during reactivity of cells, tissues and organs in determining cell division and cell growth, and to geotropic or phototropic stimuli. The entire plant is bipolar in nature consisting of two ends, ‘plumular' end (where the shoots develop) and ‘radicular' (where the roots develop). Besides, there are two other terms, ‘distal' and ‘proximal'. Distal refers to the part of the plant which is furthest from the original point of attachment i.e. the tip of the leaf or shoot or root, while proximal means nearest to the point of attachment.

 

Figure 1.1: A seedling