This section is from the book "A Guide To The Wild Flowers", by Alice Lounsberry. Also available from Amazon: A Guide to the Wild Flowers.
(Plate CII.)
Four o'clock.
White.
Fragrant, like vanilla.
The Rocky Mountains.
June, July.
Flowers: growing in dense umbel-like clusters. Involucre: of five heart-shaped, whitish bracts, thin and dry. Calyx: salver-form: the tube long, and spreading into a petal-like border; the lobes notched at the apex. Corolla: none. Stamens: two to five, included. Pistil: one. Leaves: opposite; lance-ovate, with a pair of stipules at the base. Stem: branching.
The scientific name of this flower when translated is "delicate fragrance"; and we may fitly associate the words with it in connection with its English title. In appearance it suggests much more the growth of the greenhouse than that of a hardy dweller of the Rockies. The flower opens at sunset only, when it ladens the air with its luscious perfume.

Calyx, Stamens and Pistil.
 
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