A more detailed account of the plants of great utility in one direction or another native to the tropical forests, should include plantains, bananas, and yams, the wide distribution of which, largely by human agency, throughout the torrid zone is well known. The delicious pineapple is native to the Caribbean region, and was found in the markets of the Aztecs by the early Spanish invaders, although perhaps indigenous to other lands as well. In Mexico especially, but on the borders of the tropical forest and in the drier interior, grows the agave, from which the national beverage, _pulque_, is obtained, and another species of the same peculiarly American family of plants supplies great quantities of the tough fibre known as sisal or henequen hemp, particularly on the stony, arid portions of the peninsula of Yucatan. Of interest to children especially is the fact that Mexico exports some 3,000,000 pounds of chewing-gum each year, which is obtained from a plant there growing wild. To this list of indigenous products may be added ginger, arrowroot, etc., as well as many fruits scarcely known outside the tropics, such as the mango, alligator-pear, breadfruit, and numerous others. This hasty enumeration might be greatly extended or presented in more detail, but probably enough has been said to indicate the great and probably as yet but partially determined economic importance of the vegetable products of the torrid portion of North America. Associated with the tropical forest, but thriving best in an advanced skirmish-line about its drier inland borders, is a group of plants indigenous to the two Americas--the strangely shaped and spinous cacti. One of these, the prickly-pear, as it is termed on account of its pear-like edible fruit, is the emblem of Mexico. A fit legend to place about this unique heraldic design would be the motto inscribed on the rattlesnake flag of colonial days in America, "Don't tread on me," as every one will appreciate who has travelled in the southwestern portion of the United States or in the upland regions of Mexico.