342 ESSENTIALS OF BOTANY 



(7) PLANTS CULTIVATED FOR ORNAMENT 



416. Many thousand species of ornamental plants are 

 cultivated in our parks, gardens, and greenhouses. 



As regards size and duration, these plants may be classed 

 into trees, shrubs and undershrubs, herbaceous perennials, 

 and annuals. A good many evergreen conifers are planted 

 for shade trees, but the number of hard-wood trees is still 

 larger.- Some of the most beautiful species, like the great- 

 flowered magnolia, are not hardy in the northern United 

 States, and many considerations, such as power to resist 

 cold, drought, insect enemies, wind storms, and other de- 

 structive agencies, all have to be taken into account in 

 making choice of shade trees for any given locality. 



Shrubs and undershrubs are cultivated for their foliage, 

 as the box and privet ; for their flowers, as Forsythia and 

 lilac ; for their fruit, as mountain ash. 



With the exception of foliage plants, as some cannas, 

 Ooleus, and a small number of other common species, most 

 herbaceous plants are grown for their flowers. 



By far the larger part of our cultivated ornamental plants 

 are natives of other countries, and some common weeds, 

 like bouncing Bet (Saponaria) and blueweed {Uchium), have 

 become introduced by cultivation. Tropical plants are of 

 course usually cultivated only in greenhouses, and the 

 list of these is a very long one, including among the rarest 

 and most beautiful species many of the Orchis family. Of 

 our native species common in cultivation perhaps the most 

 beautiful shrubs are several azaleas and Rhododendrons 

 of the Heath family, and the most showy late summer- 

 and autumn-blooming plants are several Compositcc, such as 

 Rudheckia, Coreopsis, and Helimithus (the sunflowers). 



