ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 773 
oxylon cortex; rt., outer limit of cortex of root ; cy., its central cylinder, 
with abundant secondary wood. x about 15. O.N. 1883 (see p. 734). 
‘Photograph 10. Another root from the same preparation ; it has just become free 
from the stem, part of the cortex of which is seen at d.c. c., ¢., cortex of 
root ; cy., middle of its central cylinder ; br., br., two rootlets arising from 
the root. x 28. O.N. 1885 (see p. 734). 
PLATE 20. 
Photograph 11. Transverse section of a young root, before secondary growth has 
begun. ., cortex of root; e.c., external cortical layer ; cy., the pentarch 
stele, in which the alternating xylem and phloém-strands are seen. The 
cortex is full of secretory sacs. x about 30. C.N. 1634 (see p. 736). 
Photograph 12. Transverse section of a root branching. 6r., br., two rootlets, 
arising opposite two of the protoxylem-groups, of which there are six in all, 
two being lettered pa. ; x.®, secondary wood, beginning to form between the 
protoxylem-groups. x about 30. C.N. 1899 (see pp. 738 and 740). 
Photograph 13. Transverse section of a pentarch root, with secondary thickening. 
pe., the five protoxylem-groups, to each of which a ray corresponds ; ph., a 
phloém-group ; 2.®, secondary wood ; cb:, cambium ; ¢., outer limit of cortex. 
xX about 30. C.N. 1631 (see p. 739). 
Photograph 14. Transverse section of a very advanced tetrarch root. pz., the four 
protoxylem-groups ; ph., a phloém-group, in which the primary phloém is 
very distinct ; x.*, secondary wood ; cb., cambium ; c., outer limits of cortex. 
X about 20. C.N. 1632 (see p. 739). 
Photograph 15. Longitudinal median section of a root, giving off two rootlets. 
br., br., the two rootlets ; c., cortex of main root; 2, xylem of its stele. 
Xx about 12. C.N. 1899 (see p. 740). 
Plates 21-29.—Figures from camera-lucida drawings by Mr. Grorce BREBNER. 
Plates 21-25.—lLyginodendron Oldhamium. 
PLATE 21. 
Fig. 1. Transverse section of a very well-preserved stem. The Dictyoxylon cortex 
shows dilatation conspicuously. Next comes the inner cortex. pd., peri- 
derm, at outer limit of pericycle ; /t.!-/t.°, five leaf-traces passing through 
the pericycle, numbered in order from within outwards; their arrange- 
ment corresponds to a 3 phyllotaxis; ph., one of the primary phloém- 
groups ; secondary phloém and cambium shown; within these is the wide 
secondary wood ; w., one of the eight perimedullary xylem-strands ; pith and 
