PDF - Wallace Online

n EQUATORIAL VEGETATION 255up the smooth bark of large trees, sending out roots as theyascend which clasp around the trunk. Some mount straightup, others wind round the supporting trunks, and their large,handsome, and often highly remarkable leaves, which spreadout profusely all along the stem, render them one of the moststriking forms of vegetation which adorn the damper and moreluxuriant parts of the tropical forests of both hemispheres.Screw-pinesThese singular plants, constituting the family Pandanaceasof botanists, are very abundant in many parts of the Easterntropics, 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 arelarge and palm-like, and it is a curious sight to stand underthese and look up at the huge vegetable screw formed bythe bases of the long, drooping leaves. Some have slenderbranched trunks, which send out aerial roots ;others arestemless, consisting of an immense spiral cluster of stiff leavesten or twelve feet long and only two or three inches wide.They abound most in sandy islands, while the larger speciesgrow in swampy forests. Their large-clustered fruits, somethinglike pine-apples, are often of a red colour; and theirlong, stiff leaves are of great use for covering boxes and forother domestic uses.OrchidsmanyThese interesting plants, so well known from the ardourwith which they are cultivated on account of their beautifuland singular flowers, are pre-eminently tropical, and areprobably more abundant in the mountains of the equatorialzone than in any other region. Here they are almost omnipresentin some of their countless forms. They grow on thestems, in the forks or on the branches of trees ; they aboundon fallen trunks ; they spread over rocks, or hang down theface of precipices; while some, like our northern species,grow on the ground among grass and herbage. Some treeswhose bark is especially well adapted for their support arecrowded with them, and these form natural orchid-gardens.Some orchids are particularly fond of the decaying leaf-stalks