BICOTYLEDONES. 197 



both varieties of the former ; also common garden Spinach 

 {Spinacia, oleracea), and several species of Chenipodium, 

 as Quinoa, {G. Quinoa) an important article of food in 

 Peru and Chili, and Wormseed (C. ambrosioides), from 

 Tropical America, used in medicine. 



15. Polygonaceae. The Buckwheat family consists 

 of herbs and shrubs, rarely trees, with knotted-jointed 

 stems, and sheathing stipules, or ochrese (Fig. 306). They 

 are mostly found, in temperate regions, and number about 

 six hundred species. Representatives of this family 

 furnish the Pie-plant {Rheum Bhaponticum), from Western 

 Asia ; the Ehubarb (B. officinale), from Southeastern Asia ; 

 and the Buckwheat {Fagopyrum eseulenhmi), 

 from Central or Northern Asia. Much tannin 

 is contained in the leaves of Polygonum anvphi- 

 hium, var. terrestre, a native of the United 

 States ; and they have been occasionally used 

 as a substitute for bark in the process' of 

 tanning. 



193. The Gamopetalae are Dicotyledons, or Exogenous 

 plants, whose flowers generally have both sepals and petals 

 present, and the latter connately united. Of this group 

 the following are the most interesting or important families : 



I. Labiatae. The Mint family has about twenty-five 

 hundred species, widely distributed, except in cool regions. 

 The plants are aromatic herbs, or shrubs, with square 

 stems, opposite leaves, a deeply: four-parted ovary, and 

 often labiate flowers. The family is of no great economic 

 importance. Lavender {^Lavendula vera), a shrub of South 

 Europe, yields, on distillation. Oil of Lavender.. In the 

 same manner Oil of Peppermint is obtained from Mentha 



Fig. 306. Ochrea of Polygonum, 



