The disk florets mostly contain both stamens and pistil, while the ray florets in one series are all male.
"Wild Flowers Worth Knowing" by Neltje Blanchan
Each one has a single ray of shining white florets, narrow and separate.
"Hardy Perennials and Old Fashioned Flowers" by John Wood
Nature is slyly freakish at times, and in this instance she changed the individual flowers into ray florets.
"Making a Garden of Perennials" by W. C. Egan
The ray-florets curve inwards and "close" the flower-head in dull weather and towards evening.
"Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 9" by Various