2.1. Preparation of PPE. PPE was prepared from dried leaf
powder of Croton stellatopilosus Ohba by modifying a previously
described method [7]. The leaf powder was refluxed
with 95% ethanol (1 : 1 ratio by weight) at 70∘C for 1h. After
filtration, the extract was concentrated by using a rotary
evaporator, followed by partitioning with hexane (ratio of
1 : 1) to remove highly nonpolar constituents.With plaunotol
remaining in ethanol layer, the ethanol was evaporated in a
vacuum to obtain PPE, which was then collected and stored
at 4∘C. For use in this toxicity study, PPE was suspended in a
0.5% tragacanth solution and adjusted to various concentrations
as indicated.