490 BUCK-WHEAT TRIBE. LAUREL TRIBE. 



contains a considerable quantity of mealy albumen, which is 

 incieased by cultivation to such a degree, as to make it in some 

 species worth raising, especially as these plants will usually grow 

 on the poorest soils. The juices of these plants, however, are 

 astringent and sometimes purgative, occasionally also possessing 

 acidity. But in general these properties are diffused in no 

 large amount through their substance ; so as not to be easily 

 available. The chief medicinal product afforded by this order, 

 is Rhubarb, which is the root or rhizoma of one or more species 

 of Rheum, and is best obtained from warm countries, though it 

 has been produced in Britain. The garden Rhubarb of this 

 country corresponds with the common Sorrel and Dock, which 

 also belong to this order, in the acidity of its leaves and leaf- 

 stalks, on account of which it is cultivated. The Polygonum 

 bistorta^ or Bistort, so named on account of the twice-twisted 

 form of its roots, is one of the most powerful of vegetable 

 astringents; and the roots abound in starchy matter, which, 

 when the tan has been separated, may be used as food. The 

 Polygonum fagopyrum, or Buck-wheat, should more properly be 

 called Beech-wheat; since it derives both its scientific and its 

 common name from the resemblance between its seeds and beech- 

 mast. In China and many parts of the East, it has long been 

 cultivated as a bread-corn, and it was introduced into Europe 

 by the Crusaders ; it is not grown to nearly the same extent in 

 this country as on the Continent. 



667. The next order, LAURINE.E, or Laurel tribe, is almost 

 entirely confined to tropical climates ; and is chiefly interesting 

 on account of the number of valuable products which it yields. 

 The Common Bay is the most northern species ; and this does 

 not naturally grow in countries more temperate than those of the 

 south of Europe. The order is easily known from those allied to it, 

 by the mode of bursting of the anthers, which open by valves 

 in the same manner as those of the Berberry (Fig. 80, . 433). 

 The perianth consists of four to six portions, arranged in an im- 

 bricated manner ; at its base are attached the stamens, which are 

 usually twice the number of its sequents. The ovarium is one- 

 celled, containing one or two pendulous ovules ; and it is sur- 



