DICOTYLEDONS: SYMPETAL^J 



313 



should be recognized as Sympetalse, are honeysuckle, elder, 

 lobelia, bluebell, primrose, morning-glory, lilac, milkweed, 

 gentian, phlox, mullein, snapdragon, and verbena. Some 

 additional prominently useful plants are as follows: 



Sweet potato belongs to the same genus (Ipomcea) as the 

 morning-glory, having long trailing stems and clusters of 

 the well-known large oblong or elongated roots. It is not 

 known whether it is native to the East Indies or America, 

 but it is extensively cultivated in all warm countries. In 

 the United States the cultivation of the sweet potato as a 

 commercial crop is confined almost exclusively to the South- 

 ern States, but important areas are found also in New Jer- 

 sey, Ohio, Indiana, and 

 Illinois. The varieties 

 called yams in the South 

 are all sweet potatoes, 

 and the name really be- 

 longs to a very different 

 plant. 



Olive. The olive-tree 

 has been known and cul- 

 tivated from the most 

 ancient times, and has 

 entered largely into the 

 life and customs of Med- 

 iterranean peoples (Fig. 

 300). It is thought to 

 be a native of southern 

 Europe and Asia Minor, 

 and thrives best in dry 

 climates such as those of 

 Syria and Assyria. It is 

 cultivated also at the 



Cape of Good Hope, in Australia, and in California. It 

 is a very long-lived tree, a thousand years having been 



FIG. 300. Flowering branch of olive. 

 After BAILLON. 



