DEOSEEACE^ — POLYGALACE^. 441 



a crest. There are 21 known genera, and about 300 species. 

 Examples — ^Viola, lonidium, Papayrola, Alsodeia. 



They are distinguished by the emetic properties of their roots, 

 which contain an active principle called violin, similar in its qualities 

 to emetin. Some species of lonidium are used in South America as 

 substitutes for Ipecacuan. The roots of Viola odorata, the Sweet or 

 March Violet, the 'lov of the Greeks, have been used medicinally as an 

 emetic j the petals are laxative, and are used in the form of infu- 

 sion mixed with sugar ; and a violet or purple colouring matter is 

 procured from them, which is employed as a test for acids and 

 alkalies, being changed into red by the former, and into green by the 

 latter. Viola tricolor, Heart's ease, and other species, have been used 

 as demulcent expectorants. V. tricolor is the origin of all the culti- 

 vated varieties of pansy. 



Order 18. — Dkoserace^, the Sundew Family. (Polypet. Hypog.) 

 Sepals 5, persistent, equal ; aestivation imbricated. Petals 5, hypo- 

 gynous. Stamens free, withering, alternate with the petals, or 10 or 

 more ; anthers bilocular, with longitudinal dehiscence. Ovary single ; 

 styles usually 3-5 ; sometimes 1 or wanting. Fruit, a unilocular or 

 spuriously trilocular capsule, 3-5-valved, with loculicidal dehiscence, 

 occasionally indehiscent. Seeds numerous, either albuminous or ex- 

 albuminous j embryo minute and erect. — Herbaceous plants with 

 alternate leaves, usually inhabiting marshy places. They are found 

 in various parts of the world, in Europe, Australia^ North and South 

 America, South Africa, China, East Indies, etc. The order is con- 

 sidered by some as allied to Saxifragacese. There are 6 known genera, 

 and about 110 species. Examples — Drosera, DrosophyUum, Aldro- 

 vanda, Dionsea. 



The Droseras have a more or less acid taste, combined with slight 

 acridity. Some of them are said to be poisonous to cattle. Their 

 leaves are furnished with glandular capitate hairs (fig. 88, p. 32 ; fig. 

 661, p. 383), which are covered with drops of fluid in sunshine ; hence 

 the name Sundew or Eos aolis. An Italian liqueur, caUed Eossoli, 

 derives its name from a Drosera used in its manufacture. Some of 

 the Droseras have dyeing properties. The hairs of Drosera have a 

 spiral coil in their interior. They fold upon insects. (For a full 

 account of the phenomena connected with the irritability of these 

 plants, see pages 380-383). Dioncea museipula, Venus's fly-trap, is a 

 North American plant, having the laminae of the leaves in two halves, 

 each furnished with three irritable hairs, which, on being touched, 

 cause the folding of the divisions in an upward direction (fig. 660, 

 p. 380). It is insectivorous. Aldrovandra vesiculosa, an aquatic found 

 in the south of Europe, is distinguished by its whorled cellular leaves, 

 or floating bladders. 



Order 19. — Polygaiaoe^, the Milkwort FamUy. {Polypet. 



