CLASSES OF INTRODUCED PLANTS. 53 



trumpet-shaped or urn-,shapod 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 hvaline 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 heen noted in Alabama, viz, r> 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 Hora as growing without cultivation are immigrants from 

 other regions, and l)ut few of these are native in the more distant 

 parts of this continent north of Mexico. They are mostly from the 

 warmer temperate, suljtropical, 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 elasticit}'^ 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 

 'naturalised when they have taken a permanent place among indigenous 

 plants; adventive when restricted to cultivated lands or to the vicinit}^ 

 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 estaljlished 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. 



