Abstract
Leaf traces are important structures in higher plants that connect leaves and the stem vascular system. The anatomy and emission pattern of leaf traces are well studied in extant vascular plants, but remain poorly understood in fossil lineages. We quantitatively analysed the leaf traces in the late Permian conifer Ningxiaites specialis from Northwest China based on serial sections through pith, primary and secondary xylems. A complete leaf traces emission pattern of a conifer is presented for the first time from the late Palaeozoic. Three to five monarch leaf traces are grouped in clusters, arranged in a helical phyllotaxis. The leaf traces in each cluster can be divided into upper, middle and lower portions, and initiate at the pith periphery and cross the wood horizontally. The upper leaf trace increases its diameter during the first growth increment and then diminishes completely, which indicates leaf abscission at the end of the first year. The middle trace immediately bifurcates once or twice to form two or three vascular bundles. The lower trace persists as a single bundle during its entire length. The intricate leaf trace dynamics indicates this fossil plant had a novel evolutionary habit by promoting photosynthetic capability for the matured plant.
Highlights
MethodsIn order to examine the emission pattern of the leaf traces, one well-preserved wedge-shaped specimen, 60 mm high × 5 0 mm wide, including pith, primary and secondary xylem was sectioned by serial thin section technique
A better understanding of the physiological feature of a primitive Palaeozoic conifer
We present the first detailed leaf trace emission pattern, in a late Permian conifer from Northwest China
Summary
In order to examine the emission pattern of the leaf traces, one well-preserved wedge-shaped specimen, 60 mm high × 5 0 mm wide, including pith, primary and secondary xylem was sectioned by serial thin section technique. The specimen was sectioned to appropriately thin wafers using a diamond saw and the upper surfaces were ground using a grinding wheel with carborundum grit in a decreasing series of #240, #400 and. The smooth upper surfaces were attached to glass slides with Buehler EpoThinTM Epoxy Resin (20-8140-032) and EpoThinTM Epoxy Hardener (20-8142-016), and the exposed surfaces were ground to a thickness of 30–50 μ m. A total of eighteen tangential thin sections (Nos. I–XVIII) were made through the pith, primary xylem and secondary xylem with a thickness of ca 2.5 mm between each thin section
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