n EQUATORIAL VEGETATION 255 



up the smooth bark of large trees, sending out roots as they 

 ascend which clasp around the trunk. Some mount straight 

 up, others wind round the supporting trunks, and their large, 

 handsome, and often highly remarkable leaves, which spread 

 out profusely all along the stem, render them one of the most 

 striking forms of vegetation which adorn the damper and more 

 luxuriant parts of the tropical forests of both hemispheres. 



Screw-pines 



These singular plants, constituting the family Pandanaceas 

 of botanists, are very abundant in many parts of the Eastern 

 tropics, while they are comparatively scarce in America. 

 They somewhat resemble Yuccas, but have larger leaves, 

 which grow in a close spiral screw on the stem. Some are 

 large and palm-like, and it is a curious sight to stand under 

 these and look up at the huge vegetable screw formed by 

 the bases of the long, drooping leaves. Some have slender 

 branched trunks, which send out aerial roots ; others are 

 stemless, consisting of an immense spiral cluster of stiff leaves 

 ten or twelve feet long and only two or three inches wide. 

 They abound most in sandy islands, while the larger species 

 grow in swampy forests. Their large-clustered fruits, some- 

 thing like pine-apples, are often of a red colour; and their 

 long, stiff leaves are of great use for covering boxes and for 

 many other domestic uses. 



Orchids 



These interesting plants, so well known from the ardour 

 with which they are cultivated on account of their beautiful 

 and singular flowers, are pre-eminently tropical, and are 

 probably more abundant in the mountains of the equatorial 

 zone than in any other region. Here they are almost omni- 

 present in some of their countless forms. They grow on the 

 stems, in the forks or on the branches of trees ; they abound 

 on fallen trunks ; they spread over rocks, or hang down the 

 face of precipices; while some, like our northern species, 

 grow on the ground among grass and herbage. Some trees 

 whose bark is especially well adapted for their support are 

 crowded with them, and these form natural orchid-gardens. 

 Some orchids are particularly fond of the decaying leaf-stalks 



