62 Scott avid Brebner.—On Monocotyledons. 
point. Other lettering as before. Only a few endodermal cells are thick-walled, 
x 175. 
Figs. 9-17. Aristea corymbosa, Benth. 
Fig. 9. Transverse section of young stem before secondary thickening. The 
light part is the central cylinder, with its scattered bundles. The dark zone is the 
cortex. On the right the section passes near the base of a leaf. Leaf-traces are 
seen passing through the cortex, x 1 7. 
Fig. 10. Corresponding section through an old stem. lf= remains of leaf, pd= 
periderm, /=lenticel, c — cortex, cb = cambium, / 2 = secondary tissues, showing the 
two zones. t x = primary cylinder, outer part shaded to indicate sclerosis. All 
reference lines run to outer limit of zone indicated, x 17. 
Fig. 11. Transverse section 2 mm. from apex. Outer part of cylinder; primary 
development in progress. Note irregular divisions of merismatic cells. The 
shaded cells in the cortex are tannin-sacs. c = cortex, m = primary merismatic 
zone or ‘Thickening Ring,’ b x — primary desmogen-strand. x 266 (reduced from 
x 400). 
Fig. 12. Transverse section 5 mm. from apex. Primary merismatic divisions 
have ceased. Primary bundles shown in various stages, px = protoxylem of most 
advanced bundle shown. Other lettering as before, x 266 (reduced from x 400). 
Fig. 13. Transverse section from older part of stem. Cambium in full activity. 
Note that divisions take place in more than one layer. Shading indicates probable 
limits of secondary tissue already formed. Primary parenchyma of cylinder has 
become sclerotic. c = cortex, cb = cambium, x 266 (reduced from x 400). 
Fig. 14. Transverse section showing cambium and part of outer secondary zone 
from an old stem. Secondary bundles sharply defined. pd= periderm, c x = primary 
cortex, c 2 = secondary cortex, cb = cambium, b 2 = secondary bundles, x 1 1 7. 
Fig. 15. Radial section through secondary tissues of a very old stem. No 
primary cortex. Periderm has been formed in secondary cortex. pd 2 = internal 
periderm, c 2 = secondary cortex, cb = cambium, b 2 = very young secondary bundle : 
x 2 = xylem, ph 2 — phloem of mature bundle, x 1 17 (reduced from x 175). 
Fig. 16. From a macerated preparation. /r = young tracheides, one still sur- 
rounded by desmogen-cells, the other free. Contents contracted by maceration, 
x 400. 
Fig. 17. Complete mature tracheide, shown in two halves, macerated. The 
borders of the pits are not shown, x 200 (reduced from x 400). 
