. Fossil plants : for students of botany and geology . Paleobotany. 246 COKDAITBAB [CH. Stems, i. Pith-casts. Artisia. Sternbeig. A character to which authors tend to attach excessive import- ance as a diagnostic feature is the almost invariable tendency of the parenchymatous pith of Cordaites to break up on contraction into transverse diaphragms, thus producing what is known as a discoid pith. In the stem shown in fig. 473 the pith is repre- sented by a more or less cylindrical cast characterised by fairly regular transverse ribs and narrow grooves; in the upper part. Fig. 473. Cordaites (or
. Fossil plants : for students of botany and geology . Paleobotany. 246 COKDAITBAB [CH. Stems, i. Pith-casts. Artisia. Sternbeig. A character to which authors tend to attach excessive import- ance as a diagnostic feature is the almost invariable tendency of the parenchymatous pith of Cordaites to break up on contraction into transverse diaphragms, thus producing what is known as a discoid pith. In the stem shown in fig. 473 the pith is repre- sented by a more or less cylindrical cast characterised by fairly regular transverse ribs and narrow grooves; in the upper part. Fig. 473. Cordaites (or Mesoxylont) stem showing the discoid pith partially enclosed by wood. (^ nat. size.) M. S. of the fossil the peripheral tissue of the pith is preserve^ in the form of narrow plates projecting from the inner face of the wood. As Eenault^ pointed out, this type of pith is the expression of certain conditions of growth and is not a satisfactory distinguishing feature of any particular genus or family. The same tendency to form a discoid pith is characteristic of Mesoxylon, and it occurs also in some other Palaeozoic genera. Corda long ago figured a stem attributed by him to Lomatofloyos with a typical discoid pith, and a similar pith is recorded in a stem of Dicrano'phyllum^. Among recent plants Juglans regia affords perhaps the most familiar instance of an identical form of pith: the same type 1 Eenault (79) B. p. 287. == Benault and Zeiller (88) A. PI. 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 Seward, A. C. (Albert Charles), 1863-1941. Cambridge : University Press
Size: 1508px × 1656px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishercambr, bookyear1898
