BICOTYLEDONES. 191 



6. Piperaceae. The Pepper family is almost con- 

 fined to the Tropics. The plants are herbs, shrubs, or 

 small trees, with spiked flowers, and generally provided 

 Avith a pungent and aromatic principle. There are over a 

 thousand species, six hundred and twenty of which are 

 included in the genus Piper, and three hundred and eighty- 

 two in the genus Piperomia. A climbing plant {Piper 

 nigrum) of East India, now cultivated also in the West 

 Indies, with heart-shaped leaves and spikes of berries, 

 furnishes the pepper of commerce. The fruit, gathered 

 green and dried, constitutes the black pepper; gathered 

 ripe and dried, it is the white pepper. The dried, unripe 

 berries of P. cubeba, of the East Indies, constitute cubebs. 



7. Euphorbiaceffi. Spurge family. A large and im- 

 portant group of three thousand species, varying in size from 

 small herbs to gigantic trees, and having a wide geograph- 

 ical distribution, though most numerous in the Tropics. 

 They generally have a milky or watery (mostly acrid and 

 poisonous) juice, and a free three-celled ovary. Arrow- 

 root is furnished by Manihot palmata and M. altissima; 

 these slender plants (of Tropical America) have thick roots, 

 containing much starch, called, when separated, arrow- 

 root ; this, when heated on hot plates and granulated, is 

 called tapioca ; the dried pulp without separation of the 

 starch is cassava. These three products are important 

 articles of food in the country in which they are produced, 

 and are exported into this country. The Castor-Oil Plant 

 (Rieinus communis), a native of India, is extensively 

 cultivated for its seeds, from which castor-oil is obtained 

 by pressure (Fig. 302). In Germany its leaves are fed to 

 silk-worms. It also occurs in cultivation as an ornamental 

 plant. From the seeds of Croton Tiglium, a plant of India, 



