In this article we will discuss about the classification of meristem based on function. The categories are: 1. Protoderm 2. Procambium 3. Ground Meristem.
Category # 1. Protoderm:
The formation of dermal tissue system in plant is attributable to protoderm. Dermal tissue system consists of epidermis/multiple epidermises and all other structures that occur on epidermis, e.g. stomata, hairs, glandular hairs etc.
Category # 2. Procambium:
The formation of vascular tissue system in plants is attributable to procambium. Procambium consists of cells that are elongated in the longitudinal plane of axis. The cells are densely cytoplasmic and contain large nucleus, proplastids and exhibit the usual features of meristematic cells. The cells are highly meristematic and undergo frequent mitoses.
The peripheral derivatives of procambium are primary phloem and the inner derivatives are primary xylem. Primary phloem and primary xylem collectively form the collateral closed vascular bundle of monocot stem. In dicotyledonous stem procambium is not completely used up in the formation of primary xylem and primary phloem.
A portion of procambium remains in between primary phloem and xylem and this portion of procambium later differentiate into cambium. Cambium with peripheral phloem and inner xylem forms the collateral open vascular bundle of dicotyledonous stem.
Category # 3. Ground Meristem:
Ground meristem represents the undifferentiated meristematic tissue of primary meristem from where ‘protoderm and primary procambial strands have been segregated’- Haberlandt (1914).
Ground meristem divides frequently and the derivatives differentiate into cortex, pith and other tissues that are associated with them. Ground meristem is regarded as the precursor of fundamental or ground tissue system. Mesophyll cells of leaf and additional procambial bundles also originate from ground meristem.
The cells of an apical meristem give rise to protoderm, procambium and ground meristem that in turn give rise to particular tissues. The tissues mature and compose the primary body of a plant.
In most terrestrial dicotyledons at the end of primary growth, additional secondary tissues are formed. The formation of primary and secondary tissues is diagramed in Fig. 7.2 and the cell lineages of their formation are illustrated in box 7.1.
