Alfred Barton Rendle, 1911 Encyclopædia Britannica (1911)
“ At the base of the general umbel in umbelliferous plants a whorl of bracts often exists, called a general involucre, and at the base of the smaller umbels or umbellules there is a similar leafy whorl called an involucel or partial involucre. In some instances, as in fool’s-parsley, there is no general involucre, but simply an involucel; while in other cases, as in fennel or dill (fig. 15) , neither involucre nor involucel is developed. In Compositae the name involucre is applied to the bracts surrounding the head of flowers (fig. 2, i) , as in marigold, dandelion, daisy, artichoke. ”
