CACTUS (Lat., from Gk. kaktos). A general name given to the peculiar plants which belong to the family Cactacea'. These plants have been specially adapted to the arid regions of America. They are chiefly displayed in Mexico, but are very abundant also along the Mexican border of the United States, and some of them extend even far north on the plains. They are also found to some extent more east ward, in the \Vest Indies, and also southward in South America. Aside from a few African spe cies, the 1000 known forms are restricted to America. However, the common prickly pear, a species of Opuntia, has been long naturalized throughout the Mediterranean region, where its fruit is known as the `Indian fig.' The peculiar habit of the family seems to have been the result of perennial drouth conditions, to which they have become better adapted, per haps, than any other plant forms. The two fold problem which is presented to them is to prevent any unnecessary loss of water contained in their tissues, and to retain all of the scanty supply which reaches them. As a result, their bodies are very succulent, containing a large amount of water-storage tissue, which retains water with great tenacity. Their bodies are also very much reduced in surface exposure, leaves being abandoned, and the stem often as suming cylindrical to globular forms. The globular form is perhaps the most complete an swer to the problem of reducing surface ex posure and retaining mass. Instead of leaves and branches which appear upon ordinary plants, the cactus forms display various ephem eral or abortive structures, the most notable of which are the bristles and pines. The cactus forms are not all of compact habit, for species of Pereskia are climbing and woody. with well developed leaves. The flowers of the group are usually conspicuous and remarkably brilliant in color. The largest forms are species of Cereus, with thick columnar and fluted bodies, bearing a few clumsy branches, and sometimes attaining a height of 50 or 60 feet. These tree-like col
umnar forms are especially well developed in the drainage basin of the Gulf of California, and sometimes occur in extensive masses known as `eardon forests.' About twenty genera of cacti are recognized, of which only five occur in the United States. The generic lines are, however, very uncertain and shifting, so that no definite number can be given. The most common genera are as follows: Mamil laria includes the globular to short cylindrical forms, which are not ribbed, but which have prominent tubercles bearing clusters of spines. It is the largest in point of numbers of all the genera, containing nearly three hundred species. Echinocactus also contains globular to short cylindrical forms, but they are strongly ribbed, and are usually larger than any of the mmil hula forms. It is the second genus in point of numbers, containing about two hundred species. Cc reu s contains species With mostly elongated stems, which are stout, columnar, or sometimes cylindrical, and always ribbed or angled. Spe cies of Pilocerens are often seen in greenhouses. and resemble the columnar forms of Cereus, but have an abundance of white hairs instead of rigid spine:, and are frequently spoken of as 'old-man cactus.' Opuntia contains about one hundred and fifty species. and includes forms which are hranehed and jointed, the joints being flat or cylindrical. The flat-jointed forms are the well-known 'prickly pears.' Consnit: Engelmann and Bigelow, of Cac taee.v," in rnited States War Department Re ports of Exploration for Railroad to the Pacific (Washington, Is561: Kunzi, Cactus: Its His tory. Classilieation. . . . and Therapeutical Application (Albany. 1875) : Coulter. Pre/int friary Recision of the North American Species of Cactus. _4 nha Ion i m, and Lophophora (Washing ton, 1894-98) ; and Preliminary Revision of the North American Species of Erhinocactus, (Welts, and Opuntia (Washington. 1896).