Domain pattern in the cambium of young Platanus stems

In the vascular cambium of Platanus Z and S domains appear in the course of formation of the first annual ring. Their arrangement is connected with the division of the stem into nodes and internodes. In each node a domain of Z and of S type occurs. The longitudinal boundaries between them run along the middle leaf trace and on its opposite side, and the transverse boundaries lie in the nodes. Z-type domains are found on the right below the base of the nearest upper leaf, and S-type domains on the left. As the young cambium forms further rings, the size and shape of the domains changes.

Transformation of the domain pattern in the development of Fagus silvatica L. cambium

The domain pattern of cambium during the first year of its function in <i>Fagus silvatica</i> L. resembles a checkerboard. The longitudinal line along the leaf trace, its corresponding line on the opposite side of the internode and nodes comprise the domain borders. Starting from the formation of the first annual ring, this checkerboard pattern begins to undergo gradual transformation. A transitional domain pattern appears during the first few years; in each internode, due to the alternate disappearance of Z and S domains, a fragmentary domain of one type and an expanded domain of the opposite type occur in pairs. After further transformations, a regular pattern of transverse bands of domains moving along the stem appear on older stems (over ten years-old). This pattern is commonly found in other studied species of trees.

Meristematic activity of the Endodermis and the Pericycle in the primary thickening in monocotyledons: considerations on the "PTM"

This paper proposes a new interpretation for primary thickening in monocotyledons. The anatomy of the vegetative organs of the following species was examined: Cephalostemon riedelianus (Rapataceae), Cyperus papyrus (Cyperaceae), Lagenocarpus rigidus, L. junciformis (Cyperaceae), Echinodorus paniculatus (Alismataceae) and Zingiber officinale (Zingiberaceae). The endodermis with meristematic activity was observed in the root of all the species, in the stem of Cyperus, Cephalostemum and Lagenocarpus rigidus, and in the leaf trace of Cyperus and leaf of Echinodorus. Considering the continuity of tissues through the root, stem and leaf, the authors conclude that in the stem the pericycle remains active throughout the life of the plant as the generator of the vascular tissue. The "Primary Thickening Meristem" is in fact the pericycle plus the endodermis and its derivatives (or only the pericycle). Close to the stem apex, the assemblage of seems to be a unique meristem, giving rise to the inner cortex and vascular tissues.

Modifications structurales des faisceaux vasculaires primaires de la tige de Cordyline indivisa (Agavaceae). 1. Analyse du patron de conversion

In Cordyline indivisa Kunth, the primary bundles change from the collateral type (distal part) to the amphivasal type (proximal part). This conversion is related to the pattern of the longitudinal course of the bundles. Ontogenically, this reflects the two stages in the construction of a vascular bundle: the formation of the lower segment, characterized by its indefinite distal end and its subsequent junction with a leaf primordium. That part of the lower segment, which is amphivasal when fully differentiated, is axial in nature; its differentiation proceeds independently of the junction with the primordium. The collateral and intermediate stages are characteristic of the junction strand and that part of the lower segment having a reoriented differentiation. Since their presence depends on the junction with the primordium and is under the influence of the latter, we relate them to the leaf trace. According to our view of vascularization, each "developmental unit" consists of an axial segment which extends in a leaf trace; new axial bundles may be emitted from one part or the other. Consequently, our definition of the leaf trace is opposed to the classical one which states that the leaf traces diverge at intervals from continuous axial bundles.

Observations on Eristophyton Zalessky, Lyginorachis waltonii Calder, and Cladoxylon edromense sp. nov. from the Lower Carboniferous Cementstone Group of Scotland

ABSTRACTFifteen specimens of Eristophyton stems from the Lower Carboniferous Cementstone Group of Berwickshire and East Lothian have been examined. Three possess medullary rays comparable to E. waltonii Lacey, the others have rays like E. beinertianum (Göpp.) Zalessky. In one specimen assigned to E. waltonii a leaf-trace subdivides outside the secondary xylem to form an arc of six separate bundles. Another stem of E. waltonii has attached closely spaced petiole bases one of which is clearly identifiable as Lyginorachis with six vascular bundles arranged in an arc. Stems of Eristophyton from five localities occur associated with petioles or rachises possessing a U-shaped vascular bundle with abaxial ridges like L. waltonii Calder. As these may occur mixed with rachises agreeing with L. brownii Calder the latter is regarded as synonymous. Detached petioles found associated with E. beinertianum may possess four or six basal bundles. The evidence suggests that the U-shaped petiolar bundle passes down into four then six basal bundles and such petioles are associated with both E. waltonii and E. beinertianum. Calder (1935, pl. 1, fig. 2) showed dichotomy in the petiole bundle.In addition different rachises are known possessing a more massive U-shaped bundle but lacking sclerotic nests and sparganum outer cortex. These are assigned to Cladoxylon edromense sp. nov. Cortical nests occur in both E. waltonii and L. waltonii and may be compared with the sclerotic plates in the compressions of Diplotmema dissectum Brongn. and D. patentissimum Ett.. The evidence supports the view that Eristophyton is a pteridosperm with bifurcate fronds known as L. waltonii Calder when petrified and comparable to Diplotmema when compressed.