Detail of Nymphaea vascular tissue, endodermis and pericycle
you can see details of what
appears to be an endodermis (Casparian strips are visible in
the detail micrograph below). A pericycle occurs beneath the
endodermis. The phloem tissue is quite extensive, and
comprises vascular parenchyma cells as well as sieve tube companion
cell complexes. Companion cells are darkly-stained.
At first glance, one would interpret this as part of a root system, but this is not the case. Nymphaea petioles contain both an endodermis-like layer (stores starch, and has Casparian strips) and an associated pericycle layer. Their function is assumed to be the same as those occurring in the root system -- regulation of centrifugal and centripetal transport across the cortex and stelar boundary. EN = endodermis; Per = pericycle; PX = protoxylem; unlabelled arrows point to companion cells.