The Mode of Secondary Growth and the Three-Dimensional Structure of the Phloem in Avicennia

Publisher Website
Google Scholar
Abstract
The mode of development of successive cambia and the differentiation of cambium derivatives are unique to Avicennia [A. germinans, A. resinifera and A. germinans] and do not follow the scheme proposed for members of other families possessing included phloem. The sequence of formation of cambial derivatives and their differentiation are: there are few parenchyma cells toward the inside; the xylem is toward the inside with continued production of up to 10 files of parenchyma cells toward the outside; a ring of 1-3 sclereids thick develops, 1-3 cells from the outer limit of the secondary parenchyma files; the sclereids start to develop very early, sometimes when only 4 outer cambial derivatives have been produced; the cambium gradually ceases to function and phloem strands are formed by cell divisions in the parenchyma files, only short fragmented cambium remnants are left on the inner side of the phloem; and a new cambium develops in the most distal parenchyma file, immediately outside the sclereids. The new cambium layer originates within the outer parenchyma cells which were among the first derivatives of the previous cambium. Occasionally the sclereids do not form a complete ring and the cambium produces a conjunctive-tissue connection through that gap. The phloem strands associate in a very complicated net-like structure. There are many tangential links within the same ring and radial links through a conjunctive-tissue connection between adjacent rings.

This publication has 0 references indexed in Scilit: