714 



TEXTBOOK OF BOTANY 



Fig. 351. A heath plant (Erica), several species of which are common on the 

 moors and heaths of Europe. Often cultivated in America. 



seed plants. They are parasites on other plants. The huckleberries, blue- 

 berries, and cranberries are well known for their delicious fruits. 



The olive family ( Oleaceae ) . The members of the olive family are all 

 trees or shrubs. The principal commercial species are the olive, culti- 

 vated for its fruits; lilac, mock orange, golden bell, and privet, prized as 

 ornamentals; and species of ash, valued as timber trees of the deciduous 

 forests. 



The madder family (Riibiaceae). This family comprises some 400 

 genera and over 5000 species, widely distributed. Common examples 

 of the wild representatives are buttonbush (Fig. 352), the bedstraws, 

 and the partridgeberry. Commercially valuable plants are coffee, the 

 ornamental gardenia, and cinchona, the source of the alkaloid quinine. 



The morning-glory family (Convolvulaceae) . The members of the 

 morning-glory family are largely trailing and climbing herbaceous vines. 

 They are distributed throughout the world, but are most abundant in 

 the tropics. Familiar examples are the bindweed, morning glory, moon 

 flower, and sweet potato. The sweet potato with its thickened roots is 

 commercially the most important plant of the family. The more watery 

 sweet potatoes are often called "yams," but the true yam is a monocot. 

 There are some 50 genera and about 1000 species. 



The mint family (Labiatae). The appearance and fragrance of most 



