Protsambiumi

Protsambiumi is a term used in botany to denote an embryonic or primordium layer that gives rise to the vascular cambium during the development of vascular plants. The term is not universally used in English-language texts and may appear in regional or historical literature. Etymology combines proto- meaning first with sambium, reflecting its proposed role as an initial cambial precursor.

In the standard view of plant primary growth, procambium forms primary xylem and primary phloem. As stems and roots transition to secondary growth, a meristematic layer derived from or associated with procambial tissue can organize into a protosambial zone that then differentiates into the vascular cambium. The protsambial tissue is typically described as comprising relatively undifferentiated parenchyma cells with the capacity to divide and differentiate into cambial initials, their derivatives, and associated ray cells. Through this process, the protosambium contributes to the initiation and patterning of secondary vascular tissues, supporting increased production of xylem and phloem during secondary growth.

The concept and recognition of a discrete protosambial layer can vary among plant lineages. In many discussions, the shift from procambium to cambium is described without naming a separate protosambial stage. As a result, protsambiumi is best understood as a historical or regional term reflecting an early cambial precursor state rather than a universally standardized anatomical label. See also procambium, vascular cambium, secondary growth, interfascicular cambium.