. Studies in fossil botany . Paleobotany. 406 STUDIES IN FOSSIL BOTANY exactly in structure with one of the primary strands of xylem in Lyginodendron (compare Fig. 156 with Fig. 131). The smallest elements of the cluster are internal, lying at a short distance from its outer limit (Fig. 156, px) ; these smallest elements are shown by longitudinal sections to be tracheides, with a lax spiral thicken- ing ; they thus constitute the protoxylem of the bundle (Fig. 1 5 7,px). They are succeeded towards the exterior by more densely spiral or reticulate trach- eides, of somewhat larger size (Figs. 15
. Studies in fossil botany . Paleobotany. 406 STUDIES IN FOSSIL BOTANY exactly in structure with one of the primary strands of xylem in Lyginodendron (compare Fig. 156 with Fig. 131). The smallest elements of the cluster are internal, lying at a short distance from its outer limit (Fig. 156, px) ; these smallest elements are shown by longitudinal sections to be tracheides, with a lax spiral thicken- ing ; they thus constitute the protoxylem of the bundle (Fig. 1 5 7,px). They are succeeded towards the exterior by more densely spiral or reticulate trach- eides, of somewhat larger size (Figs. 156 and 157, x1). The protoxylem is accompanied by a little parenchyma, and the rest of the primary strand, includ- ing all its lateral and interior part, is formed of large tracheides, with multiseriate. Fig. 157.âCorresponding longitudinal sec- tion, showing the structure of the tracheides. .rV parenchyma at the bordered pits, aS in LyginO commencement of a medullary ray. â yo Other lettering as in Fig. 156. X 135. Phil. Trans., W. and S. Will. Coll. 1266. dendron (Figs. 156 and 157, x). Similar pitted elements extend throughout the whole interior of the stele, forming the mass of primary wood. The central wood, as dis- tinguished from the peripheral xylem-strands, may be termed the metaxylem. From the nature of the case, the primary strands are not obviously distinct, as in the former genus, but they are characterised at once by their mesarch structure, and by the fact that they alone. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Scott, Dukinfield Henry, 1854-1934. London, A. and C. Black
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