Darbi shire* — Observations on Mamillaria elongata . 415 
Fig. 9. A stoma from the epidermis of the tubercle. Cuticle (y), epidermis ( e ) with the two 
guard-cells, hypoderma (i d ), and a few palisade-cells (/), with air-spaces (z) can be noticed 
x 430. 
Fig. 10. Transverse section of a tubercle low down. The radiating lines mark the rows of 
palisade-cells. Five small cortical and seven larger central bundles can be distinguished, x 5. 
Fig. 11. The same higher up. The inner central bundles are forming a circle, x 5. 
Fig. 12. The same higher up. The central bundles have closed in still more. Of the cortical 
ones only two are left, x 5. 
Fig. 13. The same higher up. The cortical bundles have come to an end. The central 
bundles have closed in still more, but fourteen bast-portions are still shown by dark dots in the bundle- 
ring. x 5. 
Fig. 14. The same higher up. The bast has disappeared; the small crosses mark the old 
wood-portions, as distinguished from the storage tracheids. x 5. 
Fig. 15. A tubercle in longitudinal and vertical section. The following structures can be made 
out : cuticle (y), epidermis ( e ) with stomata, hypoderma ( d ), palisade-cells (/), air-spaces (a), 
cortical bundles, central bundles ending in the storage tracheids (*:), bast ( a ), the cork layer 
(g and k ) separating off the spines with their core containing air ( h ), the hairs in between (i). 
X 30. 
Fig. 16. A marginal spine, with air-containing core ( h ) at the lower end. x 30. 
Fig. 17. Transverse section of a large central spine showing the air-containing core {h ). x 30. 
Fig. 18. The growing apex of a young plant. The developing tubercles with spines and hairs 
are seen. The upright position of the tubercles at first can be noticed and their gradual bending 
outwards. The actual growing point is well protected by the paraheliodes formed by the spine and 
hairs, x 6. 
Fig. 19. A few spiral tracheids ( b ) and storage tracheids ( c ) of a central bundle of the tubercle 
seen in longitudinal view, x 160. 
Fig. 20. Apical portion of tubercle, in longitudinal section, showing the multicellular hairs (z), 
the air- containing fibres ( h ) of the spine, the cork ( k ) underlying the spine, the cork cambium ( g), 
and the storage tracheid endings (c) of the central bundles of the tubercle, x 1 50. 
PLATE XXVI. 
Fig. 21. Transverse section across a bundle of the main axis. Cortex ( s ), protophloem (<?), 
bast-parenchyma (/), cambium ( r ), wood-parenchyma annular tracheids of the metaxylem ( m ), 
and of the protoxylem (/) can be made out. x 60. 
Fig. 22. Portion of the same. x 130. 
Fig. 23. The wood-portion of a similar bundle in longitudinal section. Spiral tracheids (m) 
and wood-parenchyma can be made out. x 130. 
Fig. 24. Transverse section of a bundle low down in the whole plant : wood-parenchyma («), 
spiral tracheids (m), libriform cells ( q ). x 130. 
Fig. 25. A similar portion in longitudinal section, x 130. 
Fig. 26. Two adjoining libriform cells in longitudinal section, x 360. 
Fig. 27. Portion of the cork layer low down on the plant : cork (k), cork cambium (g), 
cortex (j). x 130. 
Fig. 28. Transverse section of a spine low down : epidermis ( e ), thick-walled fibres (*), air- 
containing fibres in the centre (h). x 360. 
Fig. 29. The outer layers of a spine higher up : epidermis ( e ) and thick- walled fibres (f). x 360. 
Fig. 30. The same further in : thick-walled fibres ( t ), and air- containing fibres ( h ). x 360. 
Fig. 31. Transverse section across young root : cork (/&), cortex (s), bast-parenchyma (/), 
protophloem (0), cambium ( r ), annular tracheids of metaxylem ( m ), wood-parenchyma (?z), annular 
tracheids of protoxylem (/). x 130. 
Fig. 32. The same in longitudinal section, x 130. 
Fi g- 33- Transverse section of young root : cork (/ k ), bast (a), metaxylem (w), protoxylem (/), 
and medullary ray ( u ). x 15. 
Fig. 34. The same but older, x 15. 
Fig- 35- The same but older, x 15. 
