Pyrethri Flores. Pyrethrum Flowers.
Related entry: Pyrethrum root
Synonym.—Insect Flowers.
Pyrethrum flowers consist of the dried unexpanded flower-heads of Chrysanthemum cinerariaefolium, Vis. (Pyrethrum cinerariaefolium, Trev.), and of C. coccineum, Willd., also known as C. roseum, Web. et Mohr (N.O. Compositae). The first-named species yields the Dalmatian, the latter the Persian or Caucasian drug. The Dalmatian plant, which furnishes the bulk of the insect flowers of commerce, is indigenous to, and cultivated in, Dalmatia and Montenegro, the wild Montenegrin flowers being the most esteemed. The flower-heads are cut off just below the involucre, before they expand, and dried, being much less active when fully expanded. Persian insect flowers are seldom imported. They are distinguished by the dark involucral bracts, and by the ten-ribbed fruits; and are said to be inferior to the Dalmatian insect flowers. Three varieties of Dalmatian insect flowers are known in commerce, viz., closed, half closed, and open, the first-named being the most valuable. These are yellowish-brown in colour, and broadly conical or nearly globular in shape, being crowned with the yellowish, shrivelled, ligulate corollas of the ray florets. On the outside are two or three rows of yellowish lanceolate bracts; these are succeeded by a single row of ray florets, the centre being occupied by a large number of disc florets. The latter have a short, yellow corolla, the calyx is membranous, and crowns a five-ribbed fruit, on which shining glands can be seen with a lens. Half-closed flowers are nearly hemispherical in shape, the ligulate corollas spreading rather more, While open flowers are almost basin-shaped, and many of the ligulate corollas have been broken off and lie loose in the package. Good Dalmatian flowers yield about 8 or 9 per cent. of ash, and contain about 10 per cent. of moisture. They should yield to ether from 7.5 to 10.5 per cent. of a yellow extract. Half-closed flowers yield from 6 to 7 per cent. of extract, and open flowers from 5 to 6 per cent. If much stem is present the extract will be greenish in colour. Lead chromate, which is occasionally used to heighten the colour, maybe detected in the ash. The powder is liable to adulteration with that of other composite flowers. Its quality may be judged by the details given above, and also by the rapidity with which it stupefies small insects.
Constituents.—Closed Dalmatian flowers yield about 1.25 percent. of volatile oil, but the insecticidal properties are due to a yellow, butyraceous substance named pyrethrotoxic acid, which is not volatile, so that insect powder does not lose its activity on exposure to the air. Substances of alkaloidal and of glucosidal nature have also been found, but little definite is known concerning them.
Action and Uses.—Powdered pyrethrum flowers is used to stupefy and keep away insects. It may be dusted in their haunts as well as over articles of clothing or on the coats of domestic animals. A tincture of pyrethrum flowers (Tinctura Pyrethri Florum) is prepared with 60 per cent. alcohol (1 in 4), and is used, diluted with in parts of water, to dab on the skin to prevent insect bites.
