what is endarch and exarch ?

exarch = protoxylem towards periphery
endarch = protoxylem towards center

Endarch:when protoxylem lie inside and metaxylem grow outside.i.e in stem
Exarch;when protoxylem lie outside while metaxylem inside i.e in roots

Endarch?is the arrangement in which the?protoxylem is directed towards the centre?and?metaxylem elements towards the periphery. The?development of the xylems?in this arrangement follows the?centrifugal pattern.?It is the characteristics of the?stem of flowering plants.

Whereas?exarch?is the arrangement in which the?protoxylem is directed towards the peripheryand?metaxylem towards the centre. The?development?of the xylem in this arrangement follows the?centripetal pattern. It is the?characteristics of roots.

Endarch is the arrangement in which the protoxylem is directed towards the centre and metaxylem elements towards the periphery. The development of the xylems in this arrangement follows the centrifugal pattern. It is the characteristics of the stem of flowering plants.

Whereas exarch is the arrangement in which the protoxylem is directed towards the periphery and metaxylem towards the centre. The development of the xylem in this arrangement follows the centripetal pattern. It is the characteristics of roots.