The Cow-Tree of South America. -- We had heard of a tree, the juice of which is a nourishing milk; it is called the cow-tree; and we were assured that the negroes of the farm, who drink plentifully of this vegetable milk, consider it as a wholesome aliment. All the milky juices of plants being acrid, bitter, and, more or less, poisonous, this assertion appeared to us very extraordinary; but we found by experience, during our stay at Barbula, that the virtues of the palo de vaca had not been exaggerated. This fine tree rises like the broad-leaved star-apple. Its oblong and pointed leaves, tough and alternate, are marked by lateral ribs, prominent at the lower surface, and parallel; there are some of them ten inches long.-- We did not see the flower: the fruit is somewhat fleshy, and contains one, or sometimes two nuts. When incisions are made in the trunk of the cow-tree it yields abundance of a glutinous milk, tolerably thick, destitute of all acrimony, and of an agreeable and balmy smell. It was offered to us in the shell of the tutumo, or calabash tree. We drank considerable quantities of it in the evening before we went to bed, and very early in the morning, without feeling the least injurious effect. The ropiness of this milk alone renders it a little disagreeable. The negroes and the free people, who work in the plantations, drink it; dipping into it their bread of maize or cassava. The major-domo of the farm told us that the negroes grow sensibly fatter during the season when the palo de vaca furnishes them with most milk. Amid the great number of curious phenomena which have presented themselves to me in the course of my travels, I confess there are few which have so powerfully affected my imagination as the aspect of the cow-tree. On the barren flank of a rock grows a tree with coriaceous and dry leaves; its large woody roots can scarcely penetrate into the stone; for several months in the year not a single shower moistens its foliage; its branches appear dead and dried; but when the trunk is pierced there flows from it a sweet nourishing milk. It is at the rising of the sun that this vegetable fountain is most abundant. The blacks and natives are then seen hastening from all quarters, furnished with large bowls to receive the milk, which grows yellow and thickens at its surface. Some empty their bowls near the tree itself; others carry the juice home to their children. We seem to behold the family of a shepherd, who distributes the milk of his flock.-- Humboldt's Personal Narrative.