"Fig. 8.5. Diagrammatic representations, showing ontogenetic sequences, in cambia that have normal products (phloem to outside, xylem to inside) but abnormal conformation. Cambium produces more xylem in some places than  others to achieve flattened or lobed stems. Grooved xylem results from cambium that acts unilaterally (little or no xylem) in grooves (<i>Phaedranthus</i>); progressively, unilateral activity may expand along margins of grooves, resulting in ledged (zig-zag) appearance (<i>Passiflora</i>). Presence of xylem plates separated by rays results from sluggish cambial activity in ray areas."
"(in Fig. 8.4) Conventions for this and other figures in this chapter: <i>black</i> phloem, <i>blank</i> (with <i>circles</i> indicating vessels) xylem; <i>stippled</i> axial parenchyma, <i>vertical or variously diagonal lines in pairs</i> rays."
S Carlquist (1988)
S Carlquist (1988) p.267 Fig. 8.5. "Chapter 8. Cambial Variants (Anomalous Secondary Growth)". In: <i>Comparative Wood Anatomy</i>. Part of the series <i>Springer Series in Wood Science</i>. Springer Verlag Berlin Heidelberg.