Involucre.

Involucre. In a shortened Inflorescence (q.v.), such as the umbel, the bracts, unless suppressed, are necessarily close together, and form an apparent whorl (but really a close spiral) around the group of pedicels. This is the involucre. In compound umbels the whorl of bracts of the secondary umbel is therefore a secondary involucre, and is commonly called an involucre. In composites the crowded whorl of green leaves immediately outside the capitulum, which the non-botanist mistakes for a calyx, is constantly termed the involucre, but no less inaccurately, since here the true bracts are those of the separate florets, and occur on the surface of the capitulum itself (e.g. Finnia, Sunflower, &c.). The composite 'involucre' is therefore merely derived from those leaves of the axis below the capitulum which remain green and vegetative since bearing no florets in their axils. In Scabious (q.v.) the true bract of each floret in the capitulum unites as a sheath around the ovary, and is also known as the involucre. Here, again, we have a regrettable use of terms, themselves hardly necessary, in two distinct senses.