778 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
Fig. 29. Part of transverse section of a stem, showing what is probably a young 
adventitious root (Rt.) enclosed in the cortex. The supposed root has a 
definite stele. c¢., its outer cortex, or epidermal layer; d.c., part of the 
Dictyoaylon cortex of stem; ph., phloém; #., secondary wood. xX 50. 
C.N. 1915 (Dulesgate) (see p. 757.) 
PLATE 28. 
Figs. 30 and 31. Heterangiwm sp. 
Fig. 30. Transverse section of stem. cy., stele; a., tracheides of the xylem which 
occupies the whole interior ; x.*, secondary wood, not much developed ; ph., 
remains of phloém ; sc.’, sclerotic nests in pericycle ; ¢., cortex ; sc., sclerotic 
cortical mass ; /t., pair of leaf-trace bundles ; in the left hand one, xylem, z., 
and phloém, ph.’, can be distinguished ; Rt., a tetrarch root, perhaps con- 
nected with the stem; br, rootlet. x 18. C.N. 1804a (see p. 764). 
Fig. 31. Part of the longitudinal section of the same specimen. Lettering as before. 
The scale is too small to show the details of the tracheides, which have 
crowded bordered pits. Xx 18. C.N. 13048 (see p. 764). 
Figs. 32 and 33. Heterangium tilieoides. 
Fig. 32. Part of a transverse section of a stem, showing portions of the primary and 
secondary wood. pzx., protoxylem of one of the peripheral xylem-strands of 
the stele ; x., its centripetal, «.’, its centrifugal, primary xylem ; mz., meta- 
xylem, which extends all through the interior of the stele ; c.p., conjunctive 
parenchyma ; «.*, secondary wood; 7’, r.’, the two principal rays, limiting 
the bundle ; 7., 7., secondary rays. xX 70. OC.N. 1619 (see p. 760). 
Fig. 33. Part of transverse section of another stem, showing mesarch xylem-strand 
more in detail. Lettering as before. Note the pitting on the walls of the 
primary tracheides. Xx 150. O.N. 1801 (see p. 760). 
PLATE 29. Heterangium tilieoides. 
Fig. 34. Part of radial section of another stem passing through the corresponding 
region and showing the position of the protoxylem, pz. (here much dis- 
organized) in the xylem-strand. Lettering as in last two figures. x 150. 
C.N. 1628 (see p. 760). 
Fig. 35. Another part of the same transverse section as fig. 32, to show cambium 
and phloém. .?, secondary wood ; 1.’, principal ray ; %., 7., Secondary rays ; 
cb., cambium ; ph.°, secondary phloém ; ph., primary phloém ; pe., pericycle. 
x 70. C.N. 1619 (see p. 761). 
Fig. 36. Small part of transverse section of another stem, specially good for cambium. 
x.”, strand of secondary wood; 7., ’., secondary rays; cb., cambium ; ph.®, 
secondary phloém. x 150. C.N. 1302 (see p. 761). 
