CLASSES OF INTRODUCED PLANTS. 53 
trumpet-shaped or urn-shaped leaves of the Sarracenias. In these the 
peculiar arrangement and structure of the hairy covering on their 
inside permits the easy access of the insects to the sweet secretions 
hidden within and at the same time prevents their escape. In the sun- 
dews sensitive contractile viscid hairs cover the upper side of the 
leaves and entrap the insect upon its approach; in the bladderworts 
the hyaline bladders of the immersed leaves and stems serve as traps 
for the minute organisms swarming around them. Twenty-one spe- 
cies of insectivorous plants have been noted in Alabama, viz. 6 Sarra- 
cenias, 4 Droseras, 3 Pinguiculas, and 8 Utricularias. 
INTRODUCED PLANTS AND THEIR INFLUENCE UPON NATIVE PLANT 
ASSOCIATIONS. 
Fully one-sixth of the plants enumerated in the catalogue of the 
Alabama flora as growing without cultivation are immigrants from 
other regions, and but few of these are native in the more distant 
parts of this continent north of Mexico. They are mostly from the 
warmer temperate, subtropical, and tropical regions of the Old 
World. Those of widest distribution and which have gained the 
firmest foothold are wanderers following civilized man in his conquest 
of the wilderness. Originally children of the open plain, exposed to 
the extremes of heat, cold, drought, and excessive rain, these plants 
necessarily acquire the widest elasticity in adapting themselves to 
new surroundings and possess the greatest power of resisting adverse 
conditions. 
Considering the way these foreign plants have established and are 
maintaining themselves in their new home, they may be regarded as 
naturalized when they have taken a permanent place among indigenous 
plants; adventive when restricted to cultivated lands or to the vicinity 
of human dwellings; and fugitive when they have gained only a tem- 
porary or precarious hold on the soil. 
NATURALIZED PLANTS. 
Naturalized plants, in a strict sense (De Candolle, A. Gray), are 
those which have established themselves firmly among the native 
plants and participate in their various associations over considerable 
areas. Their introduction is in many instances due to the direct 
agency of man. About 150 species of this class have been noted in 
Alabama, the greatest number (about one-fifth) belonging to the 
grasses. Fully one-half had their home originally in central and 
western Europe; one-seventh in the Mediterranean region; one-sixth 
in the subtropical and tropical regions of the Old World; about the 
same proportion come from subtropical and tropical America (West 
Indies and Mexico to southern Brazil and Argentina); and, lastly, 
three species are from the territory west of the Mississippi and 
immediately north of Mexico. 
