ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 949 
PLATE 75. 
Sphenophyllum plurifoliatum. 
Photograph 19. Transverse section of a stem of moderate age, which has already 
cast off its primary cortex. The triarch primary xylem is shown; also the 
vadially arranged fascicular and interfascicular secondary wood and, beyond 
that, the layers of phloém and periderm. C.N. 894. xX about, 18. See also 
Plate 83, fig. 43. 
Photograph 20. Transverse section of another stem at a similar stage. The details 
of the wood and of the periderm are especially clear. C.N. 899. about 18. 
Photograph 21. Transverse section of a very advanced stem. Structure of wood 
identical with that of previous specimens, To the exterior, successive scales of 
bark are shown. C.N. 1893. x about 8. 
Photograph 22, Part of a transverse section of a still older stem, with secondary 
wood reaching 37 elements in thickness. Details of wood, especially xylem- 
parenchyma, very clear. Phloém only partially preserved, but 4 successive 
layers of periderm are present. C.N. 901. %X about 30. 
PLATE 76. 
Photograph 23. Sphenophyllum insigne. Transverse section of a stem, which still 
retains its primary cortex. Triarch primary wood has a canal at each angle. 
5-8 layers of secondary wood, with narrow medullary rays, have been formed. 
There are traces of periderm within the primary cortex. C.N. 919. x about 
30. 
Photograph 24. Sphenophyllum from Autun. Transverse section of a specimen 
presented by M. Renauur. Observe the hewarch primary xylem, which is 
imperfectly differentiated towards the centre. Secondary wood as in S. pluri- 
foliatum. C.N. 929. xX about 12. 
Photograph 25. . Part of an approximately transverse section through the strobilus 
of S. Dawsoni. The central cylinder is absent, but leaf-trace bundles, within 
the cortex, are well shown. Several sporangia show attachment to sporangio- 
phore, with its vascular bundle. C.N. 1898, H. xX about 14. 
Photograph 26. Approximately transverse section of a small strobilus of the same. 
The triangular xylem is shown in the axis. Part of the whorl of bracts seen 
is surface view, and sections of other bracts more to the exterior. One sporan- 
gium is shown attached to sporangiophore. C.N. 1898, I. x about 12. 
