Secondary Growth in Bougainvillea

The anomalous secondary growth was studied in roots and stemsof two species of Bougainvillea. The anomalous cambia arisesuccessively in centrifugal order, each originating among thederivatives of the preceding cambium. Each cambium layer functionsbidirectionally producing xylem towards the inside of the axisand phloem towards the outside. The sequence of production ofvascular cells is the following: (1) conjunctive tissue andxylem fibres towards the inside; (2) phloem towards the outside;(3) additional xylem with vessels towards the inside and additionalphloem towards the outside. The new cambia arise outside theoldest phloem cells of a given increment. This phloem may benonfunctional and crushed at that time. The phloem and the xylemdifferentiate from radially seriated derivatives produced sequentiallyby tangential divisions in the cambium. Divisions among thephloem initials and growth readjustments in the differentiatingxylem obscure the radial seriation to a moderate extent.