The cacti extend from South America northward through the lands bordering the Caribbean Sea and Gulf of Mexico, and east of the Mississippi are represented by a single genus, _Opuntia_--the prickly-pear, or Indian fig, as it is often termed--which grows in dry situations as far north as Massachusetts and Michigan. In the Great Basin several genera of cacti are plentiful, especially on dry, stony uplands, and two species reach as far northward as the Canadian boundary. Although the cacti tribe is widely distributed, the region where it presents the greatest variety and the largest individuals is in the dry, semi-desert portions of Arizona and the table-lands of central Mexico. It is most at home on sterile, rocky ridges and amid bare cliffs where there appears to be but little soil, but the strong roots strike deep into the earth in search of moisture. The cacti present great diversity of form and an indefinite differentiation of stem and leaf. In fact, there are no easily recognised leaves in the ordinary sense of the term, but the fluted and jointed stems perform the function of foliage. The plants are economical of moisture, and not only present a minimum of surface for evaporation or transpiration, but their epidermal tissues are for the most part without pores, thus retarding the escape of the moisture drawn from the seemingly dry soil. In size and shape the cacti present great variety, ranging through all gradations from the thick, strongly jointed, pad-like expansions of the prickly-pear, a few inches high, growing in widely extended clusters and massive globular forms, looking not unlike spiny melons, 2 or 3 feet or more in diameter, to jointed and fluted columns, bristling with sharp spines, the largest of which, known as the candelabrum cactus, attains a height of from 40 to 60 feet. In this the largest of all the cacti, which is not uncommon in Arizona and adjacent portions of Mexico, the central upright stem, frequently 20 inches or more in diameter, sends out from 1 to perhaps 7 or 8 club-shaped branches, which leave the parent stem nearly at right angles, but soon bend upward and become parallel with the central stalk, which they frequently surpass in height, their form thus suggesting a branching candlestick or candelabrum.