Plants may be grown from seed in flats or pots, but the seed is rare and difficult to get. Commonly young plants are purchased and grown in pots in gravelly, sandy limestone soil. Water sufficiently to keep the soil slightly moist. A bright sunny location is best. The plants are tender to frost and thrive best in warm conservatories or greenhouses. The Old Man Cactus is a popular plant for rock gardens and is found in many homes both in this country and abroad. Pipe Organ Cactus; Pitahaya (_Cereus Thurberi_) (Named in honor of George Thurber, botanist of the Mexican Boundary Commission) How to identify and how it grows These are large, columnar, symmetrical plants ten to twenty feet tall; the large columns of yellow-green stems, in six to thirty branches ascending from near the base, look much like the pipes of a great organ at a distance. The stems are from six inches to nearly two feet in diameter and are cylindrical, with fifteen to nineteen ridges lined with clusters of slender, spreading, grayish spines. The flowers, which appear only at the tips of the stems, are three inches long and half as wide, and open always at night; their delicate pink petals are suffused with green and banded in white or green, and their purple sepals are tinged with red. The fruit is very delicious, sweet and juicy, olive-green, globular, with scarlet fleshy pulp. The Pipe Organ Cactus is shown on the cover of this book. It is one of the finest of the Cactus Clan. How to grow Sow seed in sandy soil in pots or flats with partial shade; young plants may be transplanted in spring or early summer in rocky or gravelly soil and watered during dry spells once a month to moisten the soil well. The plants can be grown out of doors in the Southwest where the lowest winter temperatures are only a few degrees below freezing. In other parts of the country they may be grown indoors in rock gardens or in warm sunny conservatories. Serpent Cactus; Mexican Night Blooming Cereus; Reina de Noche (_Cereus serpentinus_) (Named specifically from the snakelike stems) How to identify and how it grows