Pericycle

pericycle [′per·ə‚sī·kəl]

(botany)

The outer boundary of the stele of plants; may not be present as a distinct layer of cells.

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Pericycle 

(also pericambium), formative tissue in the roots and the stems of plants, located around the vascular cylinder. The pericycle is represented by one or more (in gymnosperms) layers of parenchymatous cells of the meristem, which are separated from the cells of the primary cortex by the endodermis. All lateral roots develop from the pericycle of the main root. In dicotyledonous plants, action of the pericyclic cells causes the cambial cells to join in a common cylinder in the roots of secondary growth. The pericycle forms broad rays in the root, in whose parenchyma metabolic products are deposited and new adventitious roots and, sometimes, root buds are formed. When the root thickens and the primary cortex atrophies, the phellogen is differentiated in the pericycle, forming the periderm on the surface of the root.

Pericycle in the stems of plants gives rise to both sclerenchyma and parenchyma (some lianas of the families Aristolochiaceae, Cucurbitaceae, and Solanaceae) or to only sclerenchyma (in monocotyledons). In many species of Compositae (viper’s grass, dandelion), segmented latex vessels are formed in the pericycle. In Umbelliferae, essential-oil passages are formed, and in Cucurbitaceae secretory cells. In some plants of the families Liliaceae, Chenopodiaceae, and Caryophyllaceae, secondary thickening of stems and roots occurs owing to the formation from the pericycle of new layers of cambial zones and vascular bundles to the periphery of the vascular cylinder. The thickening is associated with the formative function of pericyclic cells. This type of secondary thickening of axial organs of a plant is usually called anomalous growth.

I. S. MIKHAILOVSKAIA