<Li> as part of a stelar arrangement not divided into bundles, as in many ferns . </Li> <P> In transitional stages of plants with secondary growth, the first two categories are not mutually exclusive, although usually a vascular bundle will contain primary xylem only . </P> <P> The branching pattern exhibited by xylem follows Murray's law . </P> <P> Primary xylem is formed during primary growth from procambium . It includes protoxylem and metaxylem . Metaxylem develops after the protoxylem but before secondary xylem . Metaxylem has wider vessels and tracheids than protoxylem . </P>

Give the name of the elements of xylem and phloem