On Vascular Bundle Modifications in Nodes and Internodes of Selected Grass Species

Grass nodes play an essential role as interfaces between leaf and stem. The description of the bundle course in nodes considerably contributes to understanding of the transport of assimilates, minerals, and xenobiotics in grasses. Nodes and internodes of 38 species of the subfamilies Arundinoideae, Bambusoideae, Panicoideae, and Pooideae were analyzed histologically. Free-hand sections, various staining techniques, macro- and microphotography were used to reveal a few principles underlying their anatomy. In all grass species, specific nodal zones were found in which many vascular bundles undergo characteristic transformations. This transformation starts with the augmentation of xylem in lower nodal areas and continues with the formation of specific amphivasal structures providing connections with the leaf attached to the node. The anatomy of these strands, herein called vasotubuli, has not much in common with vascular bundles in internodes any more. Transverse nodal plexus strands provide many connections between bundles and vasotubuli. The nodal plexus is also an interface of sclerenchyma bundles. The nodes of most grass species are constructed very similarly with a few exceptions: the nodes of Phragmites australis (Cav.) Steud. for example have something in common with bamboo: they develop spindle-like glomeruli.