Lyginopterids †

Tetrastichia bupatides †

• Gordon 1938

• Carboniferous of Scotland

• Stems probably scrambling in habit and with fairly long internodes

• Elliptical in transverse section owing to the very gradual disengagement of petioles, that are arranged in sub-opposite pairs and usually in four orthostichies

• Marked longitudinal mesh-work of sclerenchymatous hypoderma: mesh long and narrow, except where secondary thickening of axis causes stretching of cortical tissues, and consequent widening of the hypoderma mesh.

• Xylem cylinder 4-rayed normally, rarely 5-rayed, solid. Protoxylem of spiral or annular tracheids; metaxylem with scalariform and reticulate thickenings

• Secondary tracheids bear reticulate thickenings on both radial and tangential walls. 

• Medullary rays elongate, narrow, parenchymatous, and without ray tracheids.

• Hypodermal sclerenchyma, a network of elongated groups of fibers

• Mesh of network elongated longitudinally to stem, and meshes very narrow, except where development of secondary wood has caused tangential stretching of the mesh. 

• Median zone of outer cortex with many mucilage cells, inner zone a large-celled parenchyma without mucilage elements.

• Middle cortex usually badly preserved but containing nests of sclerotic elements. 

• Parenchyma round sclerotic nests elongated radially with respect to each.

• Petioles in nearly opposite pairs, successive pairs at right angles to one another and consequently four orthostichies of these off-sets

• Petiole bases much swollen and without hypoderma near junction with stem cortex

• Equal dichotomy of petiole some 5 in. beyond junction with stem; first pinnae on outer sides of each arm of bifurcation and normally above that bifurcation. 

• No a priori reason why primary pinnae should not depart below actual dichotomy of petiole. 

• First pinna-trace differentiated-at a low level of the petiole trace, and might easily become detached well below the bifurcation