556. Pyrethri Flores.—Insect Flowers.
556. PYRETHRI FLORES.—INSECT FLOWERS. The flowers of (1) Pyre'thrum carne'um and Pyrethrum rose'um Weber, yielding, when powdered, Persian or Caucasian Insect Powder, and (2) Pyrethrum cinerariaefo'lium Visiani, yielding Dalmatian Insect Powder, which is more powerful than the Persian powder; this latter is now produced of very superior quality in California by cultivation. The plants resemble matricaria and bear flower-heads about 38 mm. (11/2 in.) in diameter, surrounded by an imbricate involucre, (1) having brownish scales with a white scarious (membranous) edge, whitish ray-florets, and yellow disk-florets, and (2) having greenish involucral scales with scarious edge, rose-colored ray-florets, and yellow disk-florets. The flowers seldom come in market, but are in the form of a yellowish-brown or yellowish-green powder, which is used either as a powder or in tincture as an insecticide. It is not actively poisonous to human beings. Its strength or purity, and the variety from which obtained, may be ascertained by microscopical examination. A deficiency of pollen and presence of sclerenchymatous tissue would show a scarcity of flowers and the presence of stems in the powder, and consequent inferiority in strength.