Primary and secondary thickening in the stem of Cordyline fruticosa (Agavaceae)

Abstract

The growth in thickness of monocotyledon stems can be either primary, or primary and secondary. Most of the authors consider this thickening as a result of the PTM (Primary Thickening Meristem) and the STM (Secondary Thickening Meristem) activity. There are differences in the interpretation of which meristem would be responsible for primary thickening. In Cordyline fruticosa the procambium forms two types of vascular bundles: collateral leaf traces (with proto and metaxylem and proto and metaphloem), and concentric cauline bundles (with metaxylem and metaphloem). The procambium also forms the pericycle, the outermost layer of the vascular cylinder consisting of smaller and less intensely colored cells that are divided irregularly to form new vascular bundles. The pericycle continues the procambial activity, but only produces concentric cauline bundles. It was possible to conclude that the pericycle is responsible for the primary thickening of this species. Further away from the apex, the pericyclic cells undergo periclinal divisions and produce a meristematic layer: the secondary thickening meristem. The analysis of serial sections shows that the pericycle and STM are continuous in this species, and it is clear that the STM originates in the pericycle. The endodermis is acknowledged only as the innermost layer of the cortex.

Is the secondary thickening in palms always diffuse?

“…In 1984, Tomlinson´s study of the stem conducting tissues in monocotyledons reiterates that the best definition of leaf trace and axial bundle is functional, taking into account the extent to which protoxylem is differentiated; so the vascular bundle with protoxylem is functionally a leaf trace and in the axial bundle no protoxylem is differentiated. These same differences between the axial bundles and leaf traces also were observed by Menezes (1971), with the analysis of serial sections of the stem of the genus Vellozia (Velloziaceae) and Cattai and Menezes (2010) with their study in the stem of Cordyline fruticosa.…”

“…STM has been observed by various authors in the boundary between cortex and central cylinder adding parenchyma cells to the cortex, and secondary vascular bundles and parenchyma cells to the central cylinder, and can be discontinuous with the primary thickening meristem (Cheadle 1937, Lu and Chiang 1976, Stevenson 1980, Stevenson and Fisher 1980, Diggle and DeMason 1983a, b, DeMason and Wilson 1985. Recently Cattai and Menezes (2010) showed that the secondary thickening meristem has its origin from the pericycle, tissue that for these authors corresponds to the primary thickening meristem mentioned on the literature.…”

“…Although being amphivasal, the primary and secondary vascular bundles in the stem of Partesonia (Iridaceae) are the same for most of their length (Rudall, 1984). In Cordyline (DeMason andWilson 1985, Cattai andMenezes 2010) and Yucca (Diggle and DeMason 1983a, b), by contrast, the secondary vascular bundles are amphivasal, whereas the primary bundles are collateral.…”

Origin of thickening in monocotyledon stems, slope variation and population structure in a riparian forest, and the influence of seagrass beds in fish community structure

“…The debate on this subject started in the nineteenth century and is nowadays centered in the notion of a "primary thickening meristem" (PTM, for a review see Rudall 1991). Addressing this question, Cattai and Menezes (2010) determined how primary growth takes place in Cordyline fruticosa, also popularly known as cabbage palm, and how it affects the secondary thickening meristem. The authors have essentially based their study on histological cross-sections of specimens original from Asia, collected from the garden of the Instituto de Biociências.…”

Estudos morfoanatômicos em órgãos vegetativos de Cordyline fruticosa (L.) Chevalier, C. australis (G. Forst.) Endl. e C. spectabilis Kunth & Bouché

“…Devido a presença de espessamento secundário através de um "câmbio" especializado, Cordyline se distingue de outras monocotiledôneas (Tomlinson & Esler 1973) e foi utilizada como modelo em estudos anatômicos sobre espessamento dentro desse grupo por Cheadle (1937), , Fisher (1975), Tomlinson & Esler (1973), Stevenson & Fisher (1980), DeMason & Wilson (1985) e Cattai & Menezes (2010).…”