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Tans ley and Chick. — Bryophyta . 
Section II. The Histology of the Rhizome and Aerial Stem in Poly trichum. 
Fig. 12. Part of transverse section of the rhizome of P. commune. Central 
three-lobed hydrom-stereom cylinder : hyd., hydroids ; ster. , stereids ; per., pericyclic 
arc ; end., endodermal arcs. In the furrows the groups of lept., leptoids, and amyl., 
starchy tissue. Outside these, i. r. s., the inner larger cells of the radial strands ; 
hyp. st., the hypodermal strands; cor., cortex; rh., rhizoids. x 145. 
Fig. 13. Transverse section of hypoder-mal strand of same, immediately above 
point of insertion of a scale ; midrib of latter is seen to consist of thick-walled 
tissue like that of hypodermal strand. x 145- 
Fig. 14. Radial longitudinal section of same, showing insertion of scale and 
hypodermal (scale-trace) strand giving off branch which becomes midrib of scale : 
c.c., central cylinder. 
Fig. 15. Part of radial longitudinal section of same, passing through lobe of 
cylinder; references as in Fig. 12. x 245. 
PLATE IT. 
Fig. 16. Part of longitudinal section of same, passing through edge of lobe and 
furrow of cylinder ; references as in Fig. 12. x 145. 
Fig. 1 6 a Part of three leptoids from Fig. 16. x 570. 
Fig. 17. Transverse section of a leptom-strand of rhizome of same : lept., leptoids ; 
amyl., amylom; i. r. s., inner cells of radial strand. x 385. 
P'ig. 18. Transverse section of central cylinder of another rhizome of same, 
showing gradual transition from stereom to peri cycle. References as before, x 145. 
Fig. 19. Part of transverse section of rhizome of P.formosum, showing shallowness 
of furrows, absence of well-marked pericycle, angularity of hydroids, and hydroids 
abutting on endodermis; references as in Fig. 12. 
Fig. 20. Transverse section of central tissues of aerial leafy stem of P. commune, 
showing entrance of leaf-traces into the mantles of the central cylinder : cor., 
cortex; rud. per., rudimentary pericycle ; hyd., hydroids of leaf-traces ; hyd.e., peri- 
pheral hydrom -mantle ; hyd. i., thick-walled central hydroids of cylinder; lept., 
leptoids of leaf-traces and mantle ; amyl, (amylom), starchy conducting parenchyma 
of leaf-traces ; hyd. sh., hydrom-sheath. The leaf-traces are numbered from with- 
out inwards in Roman figures. 
Fig. 21. Part of radial longitudinal section of leafy aerial stem of P. commune : 
cor., cortex ; rud. per., rudimentary pericycle ; lept., typical leptoids ; hyd. sh., 
hydrom-sheath packed with starch ; hyd.e., peripheral thin-walled hydrom-mantle ; 
hyd. i., central thick-walled hydrom. x 200. 
Fig. 22. Transverse section of transitional region of P. commune', lept., showing 
the three isodiametric leptom-groups ; hyd., hydrom-strand which has now lost all 
stereids; hyd. sh., hydrom-sheath; x., small cells with starch bounding leptom- 
groups. x 230. 
