461 
in Monocotyledons ( III and IV). 
the irregular disposition of the small xylem elements in question, to say with 
certainty how far they are the result of cambial activity and how far sliding 
growth may be a factor in their origin. Some obscurity exists on this point 
in the case of Veratrum. But in Anigozanthos sp. (Fig. 5), Kniphojia caule- 
scens, Phormium tenax , and Iris sp., I have seen clear indications that these 
elements are truly secondary and are derived from the cambium. 
Figs. 1-5. Transverse sections of leaf-bundles (x 190 area), f. = fibres; px. = protoxylem ; 
mx. = metaxylem ; xy 2 . — secondary xylem ; pph . = protophloem ; ph. = phloem ; l.b. — lateral 
bundle. Figs. 1-3. Development of bundle in leaf-blade of Veratrum album L. ; Fig 1, from 
young leaf for next year still enclosed in terminal bud (August 22); Fig. 2, from leaf beginning 
to develop in succeeding spring (March 22); Fig. 3, from mature leaf (July 28). Fig. 4. Allium 
fistulosum L. Fig. 5. Anigozanthos sp. Figs. 3-5 show the mode of attachment of the xylem 
of a branch vein {l.b.) to that of the bundle from which it arises. 
Lateral veins are a relatively inconspicuous feature in the leaves of 
most Monocotyledons, but there seems to be some evidence that where 
they occur in species showing this differentiation of the xylem, their tracheal 
elements tend to be connected exclusively with the secondary wood of the 
