Periclinal

Periclinal is a term used primarily in botany to describe the orientation of a cell division plane or growth that is parallel to the surface of a plant organ. It contrasts with anticlinal divisions, which are perpendicular to the surface. The concept helps explain how plant tissues develop distinct layers and strata.

In plant development, periclinal divisions add new tissue layers rather than simply expanding a single layer. For example, in shoot and root apical meristems, periclinal divisions can contribute to forming inner tissue layers such as cortex and vascular tissues, and they can participate in secondary growth by generating new layers in the vascular cambium. The commonly cited tunica-corpus model of the shoot apical meristem describes outer tunica cells that divide mainly anticlinally to expand the surface, while periclinal divisions in the inner corpus produce deeper tissue layers.

Periclinal divisions are also central to tissue organization in epidermal and subepidermal development. They can give rise to multilayered tissues from an initially single-layered tissue, influencing organ shape and internal structure.

In genetics and plant breeding, periclinal chimeras arise when a mutation is confined to an entire cell layer (for example, the L1 layer) and that layer gives rise to most of the tissues in a resulting organ, producing a characteristic layered pattern of traits.

Overall, periclinal orientation is a key mechanism by which plants generate new tissue layers and contribute to the complexity of plant form through directional growth and differentiation.