In the very frequent cases where the bundles have considerable individuality, the fibrous pericyclic cap very clearly has a common origin from the same strand of tissue as the vascular elements themselves.
The roots of some cycads resemble the stems in producing several cambiumrings; they possess 2 to 8 protoxylem-groups, and are characterized by a broad pericyclic zone.
The external conjunctive tissue is often arranged in relation to each bundle separately, the pericyclic fibres for instance, already referred to, being cften confined to the bands of pericyclic tissue abutting on the phloem of each bundle, while the Cortex and pith frequently form rays in the intervals between the adjacent bundles.