Photograph of water lilies (Nymphea) and cross section through a root.
Water lilies belong to the category of hydrophytes. It is characterized by large and thin leaves floating at the surface of water and aerial flowers. Their roots are completely immersed.
Cross section through a root with a well-developed cortex and a small vascular cylinder in the center. The epidermis or rhizodermis is single layered and consist of thin – walled cells. The cortex possesses many air cavities (lacunae) forming an aerenchyma whose parenchyma cells are small and arranged in row around lacunae. In different places of this aerenchyma, we note the presence of sclereids in form of stars (see blue arrows) whose lignified walls offer support to the roots.
Characteristics of this section: aerenchyma and sclereids in the cortex in relation with the aquatic medium in which the plant lives; small central cylinder, large cortex and alternance of xylem and phloem three features of a monocotyledon root.
cc: central cylinder; rh: rhizodermis; x: xylem. Scale: 500 μm