Anatomical features and silica depositional patterns in the rhizomes of the grasses Sorghastrum nutans and Phragmites australis

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Abstract
Rhizomes of field-grown specimens of two grasses, Sorghastrum nutans (L.) Nash and Phragmites australis (Cav.) Trin., were prepared for anatomical study and silicon analysis using light microscopy, scanning electron microscopy, and energy dispersive X-ray microprobe analysis. Silicon deposition, as detected by the latter, was restricted in S. nutans essentially to four perivascular zones in a transect across the rhizome; two being associated with the outer vascular bundles and endodermal region of the cortex, and the other two zones with the sclerenchyma and central vascular bundles of the stele. No comparable silicon deposition was detected for P. australis, none being present above background levels both in transections and digested material of mature functional rhizomes. Contrasting aspects of silicon localization as well as differences in basic plan of rhizome anatomy exhibited by these two species are discussed in relation to differing habitat requirements and to previous root and rhizome studies.