THE TROPICAL ZONE. 191 



themselves upon trees, to which they impart a luxuriant ap- 

 pearance, as the leaves of some of the PotJws plants are of 

 an enormous size. 



An introduction to one or two more families is indispen- 

 sable ; there is a very important one called the Pandanus 

 tribe (known also by the name of Screw-pines) which when- 

 ever the soil or the atmosphere possesses a sufficient quan- 

 tity of moisture, has a decided influence on the appearance 

 of the landscape. (Plate IX.) They have, in general, long, 

 linear-lanceolate leaves of a shining green, which are placed 

 in regular spiral lines on the tall, straight, or sometimes 

 winding stems, and cover them to the top. They sometimes 

 grow in dense jungles, and frequently in loose sandy soil, 

 when they are provided with a curious and wonderful appa- 

 ratus for keeping them steady in this otherwise insecure 

 foundation ; they are supported by the aid of roots, which 

 are put out from various parts of the trunk at some height 

 from the ground, and from thence descend into the earth 

 in a slanting direction ; acting, in short, as so many but- 

 tresses. The Pandani have rather a different character 

 in the New World, where they have no stems, and feathery 

 foliage. 



The Ananas family too, of which the Pine-apple (Bro- 



