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n EQUATORIAL VEGETATION 243whose trunks are formed by a miniature forest of aerial roots,sometimes separate, sometimes matted together, are characteristicof the Eastern tropics, but appear to be rare or altogetherunknown in America, and can therefore hardly beincluded among the general characteristics of the equatorialzone.Besides the varieties of form, however, the tree-trunks ofthese forests present many peculiarities of colour and texture.The majority are rather smooth -barked, and many are ofpeculiar whitish, green, yellowish, or brown colours, or occasionallynearly black. Some are perfectly smooth, othersdeeply cracked and furrowed, while in a considerable numberthe bark splits off in flakes or hangs down in long fibrousribands. Spined or prickly trunks (except of palms) are rarein the damp equatorial forests. Turning our gaze upwardsfrom the stems to the foliage,we find two types of leaf notcommon in the temperate zone, although the great mass ofthe trees offer nothing very remarkable in this respect.First, we have many trees with large, thick, and glossy leaves,like those of the cherry -laurel or the magnolia, but evenlarger, smoother, and more symmetrical. The leaves of theAsiatic caoutchouc tree (Ficus elastica), so often cultivated inhouses, is a type of this class, which has a very fine effectamong the more ordinary-looking foliage. Contrasted withthis is the fine pinnate foliage of some of the largest foresttrees, which, seen far aloft against the sky, looks as delicate asthat of the sensitive mimosa.Forest Trees of Low GrowthThe great trees we have hitherto been describing form,however, but a portion of the forest. Beneath their loftycanopy there often exists a second forest of moderate-sizedtrees, whose crowns, perhaps forty or fifty feet high, do nottouch the lowermost branches of those above them. Theseare of course shade-loving trees, and their presence effectuallyprevents the growth of any young trees of the larger kinds,until, overcome by age and storms, some monarch of theforest falls down, and, carrying destruction in its fall, opensup a considerable space into which sun and air can penetrate.Then comes a race for existence among the seedlings of the