What are endarch and exarch conditions?
They primary xylem tissue in plants is categorized into protoxylem and metaxylem. Protoxylem is the first part of the xylem to mature first and possess small cells. The development of primary xylem can be of four types namely, exarch, endarch, centrarch and mesarch.
Endarch condition involves the development of protoxylem from the innermost procambial cells adjacent to pith. Development is inward to outward. Hence, protoxylem is found inside to metaxylem . This is considered to be centrifugal pattern of arrangement.
Exarch condition involves the development of protoxylem from the outermost edge of procambial cylinder. Development is from outside to inside. Protoxylem is found outside the metaxylem . This is considered to be centripetal pattern of arrangement.