Root: long straight rhizome, covered with scales or round stalk scars.
Stem: single, vertical, slightly bent, shooting out from middle of rhizome; dark painted.
Branches: there is the stub of a lost branch at mid-stalk.
Leaves: a single large leaf, horizontal, shaped like a very fat C, with smooth rim. Painted solid dark.
Stalk: short.
Flowers: one white flower, pointing almost straight up.
Stalk: long, light colored, with a darker vein; part of it obscured by leaf which should be behind it.
Chalyx: well-drawn, with thick tongue-shaped sepals, light colored.
Petals: well-drawn, flaring, lily shaped, serrated edges, white underpaint.
Core: not visible.
Stamen: long, with a few short hairs.
Two paragraphs (with lines, respectively), left- and
right-justified: one at the top, interrupted by the single flower,
and one just below mid-page, interrupted by the main stem.
Presumably, the flower stem was in front of the leaf in the
original drawing; but the dark overpaint covered it. The original
outline of the leaf may have been obscured, too.
The leaf shape suggests it is a water plant. With that assumption,
the choices are quite few. Rene suggested
Nymphaea candida (a.k.a. Nymphaea alba; water lily, seerose)