"Fig.8.4. Modes of interxylary phloem occurrence. Phloem strands may be very small, with only one or two sieve tubes (<i>Stylidum</i>); or larger, in bands (<i>Gaura</i>); in confluent axial parenchyma (<i>Combretum</i>); centripetal, with older phloem crushed at abaxial sides of phloem strands (<i>Strychnos</i>). Conventions for this and other figures in this chapeter: <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.265 Fig. 8.4. "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.