Giant cacti and spiny scrub abound.
In ascending from the coast-valleys there is first an arid range, where the great-branched cacti rear themselves up among the rocks.
The Cacti may be described in general terms as plants having a woody axis, overlaid with thick masses of cellular tissue forming the fleshy stems. These are extremely various in character and form, being globose, cylindrical, columnar or flattened into leafy expansions or thick joint-like divisions, the surface being either ribbed like a melon, or developed into nipple-like protuberances, or variously angular, but in the greater number of the species furnished copiously with tufts of horny spines, some of which are exceedingly keen and powerful.
Truncatum the flowers have a very different aspect from that of other Cacti, from the mouth of the tube being oblique and the segments all reflexed at the tip. The short separate pieces of which these plants are made up grow out of each other, so that the branches may be said to resemble leaves joined together endwise.
Plantations of the nopal and the tuna, which are called nopaleries, are established for the purpose of rearing this insect, the Coccus Cacti, and these often contain as many as 50,000 plants.
The most common plants of the Mexican plateau are the agaves, yuccas and cacti, each of which is represented by a number of species.
Palms are common, the chestnut abounds in many places, the cacti are almost as numerous as on the open plateau.
Cacti, euphorbias, &c.) from hot, dry and almost waterless regions where evaporation would be excessive, the leaf surface, and consequently the number of stomata, are reduced to a minimum, as it would be fatal to such plants to exhale vapour as freely in those regions as the broad-leaved plants that grow in places where there is abundance of moisture.
Proceeding southward cacti become common, first a dwarfed species, and then a larger columnar form (Cereus quisco).
It consists of the females of Coccus cacti, an insect of the family Coccidae of the order Hemiptera, which feeds upon various species of the Cactaceae, more especially the nopal plant, Opuntia coccinellifera, a native of Mexico and Peru.
The vegetation of Spain is distributed in clearly marked zones; but over the whole of Portugal, except the hottest parts of Algarve and Alemtejo, the plants of northern Europe flourish side by side with cacti, palms, aloes and tree-ferns (see Cintra).