In the Amazonian region of Brazil, there exist about 21 species of heveas; of these the principal is the hevea braziliensis, which under the name of “the Pará rubber-tree” deserves to be classed in the front rank of all the other lactiferous plants in the world. The =hevea braziliensis= furnishes the most highly esteemed quality of rubber, and it is the value of that product which determines the prices of all the other species of rubber brought on to the market. The heveas are powerful trees of from 20 to 30 metres high, the trunk which is cylindric in form and of a light ashy color, generally attains a diameter of from 0ᵐ80 to 1ᵐ20; the branches only commence to grow at about 15 metres from the ground. The leaves fall in June, but are speedily substituted by others; it is during this period that the trees break into flower. They grow in the valley of the Amazon, which within Brazil embraces the State of the Amazonas, the federal territory of Acre, almost all the State of Pará, the North of Matto Grosso and of Goyaz and a part of the South of Maranhão, or say about 5,000,000 of square kilometres. Their =habitat= as a general rule is a low and warm region whose temperature varies between 25° and 30°; without sudden changes during the course of the year and they favor by preference the watery soils, just swampy, damp and even marshy; however, at the head-waters of some rivers, they also live and develop themselves perfectly well in dry and elevated land. In the Amazonic forests, the average proportion is of one hevea-tree for 80 trees of other species. The milky latex circulates from the root to the leaves, existing, however, in greater abundancy in the trunk, up to a height of about 2 metres from the ground. The heveas in Brazil are generally known by the term “seringueiras” and the forests in which they are found are denominated “seringaes.” The average production of a “seringueira” during the harvest season, which extends over the space of 6 months, is of 5 kilos of fine rubber and 750 grs. of sernamby. The species most appreciated besides the =hevea braziliensis=, are the =hevea de terra firme=, of which Dr. E. Ule treats in his recent studies, and which are found on the frontiers of Matto Grosso, the =hevea do Rio Negro=, called “seringa verdadeira” (the real seringa), the =hevea benthamiana= and the =hevea dukei=, =Hub=, from the region of the Japurá, all of them furnishing excellent products.