The dense forests also contain many varieties of lianas or rubber vines, huge bombax and bamboos.
The density of the forest is greatly augmented by the cipos, or lianas, which overgrow the largest trees to their tops, and by a profusion of epiphytes which cover the highest branches.
These widely divergent conditions give to Mexico a flora that includes the genera and species characteristic of nearly all the zones of plant life on the western continents - the tropical jungle of the humid coastal plains with its rare cabinet-woods, dye-woods, lianas and palms; the semi-tropical and temperate mountain slopes where oak forests are to be found and wheat supplants cotton and sugar-cane; and above these the region of pine forests and pasture lands.
Its forests are not composed of one or a few dominating species, as in the cold temperate zone, but of countless genera and species closely interwoven together - a confused mass of giant trees, lianas and epiphytes struggling to reach the sunlight.
To these lianas (species of which yield one kind of the rubber of commerce) is due largely the weird aspect of the forest.
Neither can it be proved that the Huns and Magyars belonged either physically or linguistically to the same section as the lianas and Ephthalites.
The most valuable of the forest flora are the lianas, notably Landolphia florida, which yield the india-rubber of commerce.
The vegetation on the western side of the island is much less dense, often appearing as scattered clumps of trees on savannah-like plains rather than continuous forest; while in the south-west, where the rainfall is very scanty, the vegetation is largely of fleshy-leaved and spiny plants - aloes and cacti (the latter introduced), with several species of Euphorbia, as well as numerous lianas, one of which (Intisy) yields india-rubber.
In the eastern forests palms, bamboos, lianas and tree-ferns, as well as species of Dracaena, are found.
In the Ghazal province also are many rubber-producing lianas, among them the Landolphia owariensis.
Twining lianas are met with in a species of Bignonia; Umbelliferae Ranunculaceae and Cruciferae, are represented by a few fruits.
All over the forest spread lianas, or monkey-ropes, their usual position being that of immense festoons hanging from tree to tree.