Publisher's Synopsis
Excerpt from Some Characters of Xylem Tissue in Cycads, And, the Bar of Sanio and Primordial Pit in the Gymnosperms
These spool-shaped bars, extending in radial series across the lumens of adjacent tracheids, have received considerable notice in literature, owing to the confusion which arose in some cases between them and bars of Sanio. They have not before been figured in the Cycads, but are present, as shown in fig. 8, a radial section of Dioon spinulosum stem. They contain a core or axis composed Of a substance which stains in the same way as the middle lamella of the cell. This core pierces the tangential secondary walls Of the tracheid and joins up with the middle lamella. These structures are present in higher forms, but their significance is not known. Since they connect with the primary wall, they must have been laid down before the beginning of secondary thickening.
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