In the valley of the Amazon exist the =micandras=, belonging to the same family and producing a rubber of a superior quality, since it is sold under the name of Fine-Pará. The production of these trees goes to the market included in the category of hevea, owing to its similarity to this latter. The =micandra syshenoide= which is the most known species, is found on the Lower Amazon, in the innumerable islands at the estuary of the great Amazon River, in the valleys of the Madeira, the Solimões, the Japurá and the Purús; the natives give it the names of =tapurú=, =curupita=, =murupita= and =seringarana=. They are leafy trees whose trunk is of from 0ᵐ80 to 1ᵐ in diametre and from 20 to 25 metres high. They grow as well in the low lying marshy soil as in the elevated lands, whence comes their denomination of =tapurú da vargem= and =tapurú de terra firme=. The tapurú is as lactescent or milky as the hevea and the latex which it renders is equally rich, seeing that it gives 50 per cent of fine rubber. The trees whose product, the =caucho=, occupies the second place in the general exportation of rubber from Brazil although as a matter of fact it only commenced to come into the Brazilian markets in the year 1896, belong to the family of the Ulmaceas. These are the =Castillas= which up till a short time ago have been classed as of the same species as that which grows in Mexico and Central America—the Castilla elastica, but studies made by professor O. Warburg show that they are distinct species which was thence forward denominated =Castilla Ulei, Warb.= The “castillôa” is a tree of large proportions, reaching to a height of from 12 to 18 metres; its trunk with a diametre of from 0ᵐ60 to 0ᵐ90, is of an ashy gray color, smooth and sparingly branched. The leaves are large, greater, indeed, on the new plants than on the full grown trees and its fruit is of an oily nature. These trees grow in considerable quantities at the sources or head-waters of the affluents of the Amazon on the latter’s right bank, such as the Juruá, the Purús, the Madeira, the Tapajóz and the Xingú, and on its left bank in the valleys of the Japurá, the Iça, the Rio Negro and the Trombetas Rivers. Abundant “cauchaes” or forests of cautchou trees exist also in the region of the River Tocantins and of the Araguaya. The “castillôa” is found therefore in the same regions as those in which the “seringueiras” flourish; it exacts a warm climate, a clayey or clayey-silicious soil, but does not thrive in swampy ground or such as is easily inundated during the rainy season. The latex is found as much in the bark as in the alburno and each tree felled produces on an average about 50 litres of latex or say from 18 to 20 kilos of rubber.