Several natural groups or genera go to make up the Pincushion Cacti, and of these the two most important in the great desert of the Southwest are the interesting plants of Coryphantha and Mammillaria. The name “Coryphantha” alludes to the plant’s habit of bearing the flowers at its top; Mammillaria is from _mammilla_, a nipple, referring to the tubercles or knobs of the plant. They are the smallest of the large and important cactus family (Cactaceæ), the Fantastic Clan, and their stems are single or in clusters and from one to twelve inches in height and diameter, often as broad as long, or broader. Often, too, the upper surface is almost flattened, while the main part of the plant is a carrot-shaped fleshy root, which Nature, the great Builder, has made a reservoir of food and water for this, her baby of the Fantastic Clan, to withstand the drying desert winds that sweep across the mesas and up the cañons, and the months of drought and fiery heat in the desert sun, when no rains come to freshen and beautify the earth and to gladden the hearts of native dwellers on the desert. The stem is studded with tubercles spirally arranged, and each crowned with an areola bearing a cluster of slender but stout spines, often hooked like the tines on a spear; and usually with hairs. This spiral arrangement gives the plant a very attractive appearance. Some species have a thick milky juice in their stems, others a colorless watery sap. The flowers are day-blooming, both opening and closing with surprising rapidity. Mammillaria blossoms are relatively small, while those of Coryphantha are much larger, often two or three inches across; yellowish, white, pink, rose, red, or purple. There are usually many sepals, petals, and stamens, all beautifully and symmetrically arranged, and the harmony of color in the flowers is often commented upon with delight. While the flowers last at most but a few days, many of the different plants are in bloom for a considerable length of time, and some blossom two or three times a year during the spring and summer. The fruit of Pincushion Cacti are naked and smooth, rarely with a few scales in some species, and when mature red, green, yellowish, or dull purplish, and club-shaped or nearly globose. They are borne at the bases of the tubercles; in Coryphantha, at the bases of young tubercles near the top of the plant, so that they appear terminal; in Mammillaria, at the bases of old tubercles some distance from the top of the plant.