THE NUTRITION OF PLANTS 
165 
swallowed by animals. Some common illustrations are as 
follows : 
(1) Pitcher plants. In these plants the leaves form 
tubes, or urns, of various forms, which contain water, and 
to which insects are attracted and drowned (see Fig. 146). 
A pitcher plant common throughout the Southern States 
may be taken as a type (see Fig. 147). The leaves are 
shaped like slender, hollow cones, and rise in a tuft from 
the swampy ground. 
The mouth of this 
conical urn is over- 
arched and shaded 
by a hood, in which 
are translucent spots, 
like small windows. 
Around the mouth 
of the urn are 
glands, which se- 
crete a sweet liquid 
(nectar), and nectar 
drops form a trail 
down the outside of 
the urn. Inside, just 
below the rim of the 
urn, is a glazed zone, 
so smooth that insects 
cannot walk upon it. 
Below the glazed zone 
is another zone, 
thickly set with stiff, 
downward-pointing hairs, and below this is the liquid in 
the bottom of the urn. 
If a fly is attracted by the nectar drops upon this curious 
leaf, it naturally follows the trail up to the rim of the urn, 
where the nectar is abundant. If it attempts to descend 
within the urn, it slips on the glazed zone, and falls into 
FIG. 155. 
A sun-dew, showing rosette habit of 
the insect-catching leaves. 
