The Cholla has a fierce armor of thorns, long and stout, sharp and dangerous, a group of Cholla on the mesas comprising a veritable fortress of the desert. These spines are of one kind but of different sizes, and they are sheathed. On account of their sheathed thorns the Cholla are the most dangerous of all the cactus groups, and feared most of all Cactaceæ. The spines vary from an inch or less to three inches or more in length, and occasionally are half an inch or more through. The stems of these species are cylindrical, from a foot or less to fifteen feet tall, the branches generally forming into a broad rounded head. They are not ridged or fluted, but are covered with tubercles arranged spirally. The plants are often grotesque and generally resemble dwarf trees, though typically shrubby in habit. The leaves are scalelike and soon fall off. Spicules are always present, generally half an inch or so in length, easily dislodged, so easily blown off by the wind that two species of this genus are called “Jumping Cholla.” The flowers are showy and very conspicuous, large, and of all colors of the rainbow in many instances; opening and closing on the same day and at different hours in different species, rarely appearing the second day. A peculiar phenomenon is observed: the flower buds sometimes grow out from mature fruit, thus producing chains of fruit lasting for years. The fruit varies in character and is found to be tubercled or smooth or shiny, but always bearing the customary spicules. It is sometimes dry, sometimes fleshy, often remaining unchanged and edible for several years on the plants. Another curious fact is that the fruits of many species when planted in soft moist soil, or even falling to the ground, develop roots and grow into new plants, the seeds within remaining viable and capable of growth later on. [Illustration: SPINY TREE CHOLLA (Opuntia spinosior)] How to grow Most species grow readily from cuttings of one to several joints set a few inches deep in sandy soil and given enough water to keep the soil moist; it is better to allow the cut surfaces time to dry before planting. Plants can be grown also from seed planted a half-inch deep in sandy soil out of doors or in flats, with part shade and watered enough to keep the soil moist but not wet. Also, the fruits of many species when planted in moist soil develop roots and grow into plants. Cuttings or plants grow indoors or outside. A south exposure is preferable. California Cholla (_Opuntia Parryi_) (Named in honor of Dr. C. C. Parry, who first collected it in 1851) How to identify and how it grows