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, 
Coleus, 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 (Hchium), 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 Composite, such as 
Rudbeckia, Coreopsis, and Helianthus (the sunflowers). 
