In his forest wanderings, Mr. Bates was especially attracted by the colossal trees. He says that, on the whole, they had not remarkably thick stems; the great and uniform height to which they grow without throwing off a branch is a much more noticeable feature than their thickness; but at intervals he paused before a veritable giant. Only one of these huge patriarchs of the woods can flourish within a given space; it monopolizes the domain, and none but humble individuals can nestle within its shadow. The cylindrical trunks of these larger trees were generally about twenty to twenty-five feet in circumference. Von Martius, another Brazilian traveller, mentions having measured trees in the Pará district, belonging to various species (Symphonia coccinea, Lecythis spirula, and Cratæva Tapia), which were fifty to sixty feet in girth at the point where they become cylindrical! The height of the vast column-like stems could not be less than 100 feet from the ground to their lowest branch. The total height of the Pao d'Ano[152] and the Massaranduba, stem and crown together, may be computed at from 180 to 200 feet. Where one of them stands, the vast canopy of leafiness rises above the other forest trees like a domed cathedral above the minor buildings of a city. A very curious feature in these trees is the growth of buttress-shaped projections around the lower part of their stems. The spaces between these buttresses, which may be compared to thin walls of wood, form spacious chambers, like stalls in a stable; some of them large enough to hold half-a-dozen persons. "The purpose of these structures," says Mr. Bates, "is as obvious at the first glance, as that of the similar props of brickwork which support a high wall. They are not peculiar to one species, but are common to most of the larger forest trees. Their nature and manner of growth are explained when a series of young trees of different ages is examined. It is then seen that they are the roots, which have raised themselves ridge-like out of the earth; growing gradually upwards as the increasing height of the tree required augmented support. Thus they are plainly intended to sustain the massive crown and trunk in these crowded forests, where lateral growth of the roots in the earth is rendered difficult by the number of competitors."