480 A TEXT-BOOK OF BOTANY. 



probably due either to saponin or an acrid volatile principle rather 

 than to raphides of calcium oxalate. Frequently these principles 

 are dissipated or destroyed on cooking, and the plants are then 

 used as food, as the WATER ARUM (Calla palustris), which on 

 account of its acrid principles is used as a remedy for snake bites 

 when in the fresh condition, but which on drying loses- its acridity 

 and being rich in starch is used as a food (Fig. 263). To this 

 family also belong Jack-in-the-pulpit, or INDIAN TURNIP (Ari- 

 sama triphyllum), the acrid corm of which is used in medicine 

 (Fig. 261) ; SKUNK CABBAGE (Symplocarpiis fcetidus), the fetid 

 rhizome of which has medicinal properties (Fig. 262). A number 

 of plants of the Arum family are rich in starch, as the tubers of 

 Xanthosoma edule of Surinam, which contain 62 per cent, of 

 starch. 



VI. ORDER XYRIDEALES OR FARINOSE. 



The plants are mostly perennial herbs of tropical and sub- 

 tropical America. The order includes a number of families, 

 among which is BROMELIACE^E, to which the pineapple (Ananas 

 sativus) belongs. PINEAPPLE is a native of Brazil and is now cul- 

 tivated in warm countries of the eastern and western hemispheres. 

 The fruit contains a proteolytic enzyme resembling trypsin and 

 also a milk-curdling ferment. The bast fibers of the leaves are 

 used for textile purposes. Some of the Bromeliaceae are epi- 

 phytic (air-plants), the best known member being probably the 

 FLORIDA MOSS (Tillandsia usneoides), which is used in upholstery 

 (Fig. 264). 



The family Commelinaceae is represented in the United States 

 by Commelina or day-flower, some species of which have medic- 

 inal properties. The roots of some tropical species contain saponin, 

 as C. deficiens, of Brazil. The rhizomes of a number of species 

 of Commelina contain notable quantities of starch and are edible. 

 The spiderworts (Tradescantia) common in rich soil in the 

 United States, and the Wandering Jew (Tradescantia Zebrina) 

 commonly cultivated as an ornamental plant, also belong to this 

 family. To the PONTEDERIACE^: belong several perennial aquatic 

 or bog plants, whose leaves are usually thick or in some cases long 

 and grass-like. The flowers are frequently arranged in Spikes 

 subtended by leaf -like spathes (Fig. 265). 



