Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

The Evolution of Tracheid Diameter in Early Vascular Plants and Its Implications on the Hydraulic Conductance of the Primary Xylem Strand

Karl J. Niklas
Evolution
Vol. 39, No. 5 (Sep., 1985), pp. 1110-1122
DOI: 10.2307/2408738
Stable URL: http://www.jstor.org/stable/2408738
Page Count: 13
  • Read Online (Free)
  • Download ($4.00)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Evolution of Tracheid Diameter in Early Vascular Plants and Its Implications on the Hydraulic Conductance of the Primary Xylem Strand
Preview not available

Abstract

A cumulative correlation analysis of the maximum diameter of primary xylem tracheids recorded for 41 tracheophyte fossils, plotted against their ages (ranging from the Upper Silurian to the Lower Devonian), yields a Spearman rank coefficient (rsp) of 0.696 (P < 0.01). Data for specimens taxonomically referable to zosterophyllophytes and lycopods reveal an increase in the range and maximum diameter of tracheids from the Siegenian to the Emsian. Correlation analysis of these data yields an rsp value of 0.95 (P < 0.02). The mean and maximum tracheid diameters recorded for rhyniophytes, when correlated against stratigraphic occurrence, yield rsp values of 0.81 (P < 0.05) and 0.85 (P < 0.02), respectively. A correlation analysis of the data for rhyniophytes, trimerophytes and progymnosperms yields an rsp value of 0.87 (P < 0.01). Therefore, despite a relatively small sample size of early Paleozoic plants, the available data show a surprising level of statistical robustness. The data are interpreted to indicate that during the early evolution of tracheophytes, both the range and maximum tracheid diameter of the primary xylem increased, while in some plant lineages (zosterophyllophytes) there is evidence for a plateauing of maximum tracheid diameters by the Middle Devonian. The statistical trends in the data are interpreted within the context of the evolution of the hydraulic conductance of tracheophyte primary xylem.

Page Thumbnails

  • Thumbnail: Page 
1110
    1110
  • Thumbnail: Page 
1111
    1111
  • Thumbnail: Page 
1112
    1112
  • Thumbnail: Page 
1113
    1113
  • Thumbnail: Page 
1114
    1114
  • Thumbnail: Page 
1115
    1115
  • Thumbnail: Page 
1116
    1116
  • Thumbnail: Page 
1117
    1117
  • Thumbnail: Page 
1118
    1118
  • Thumbnail: Page 
1119
    1119
  • Thumbnail: Page 
1120
    1120
  • Thumbnail: Page 
1121
    1121
  • Thumbnail: Page 
1122
    1122