It is late on a sultry day in June and we are speeding along the dusty highways of Central Mexico, intent on our quest for a certain queer specimen of the weird Fantastic Clan, when the long low shadows of the afternoon begin to slant over the singular cactus growths for which we have been searching, and the blue haze of a waning day is seen to gather over the distant mountains. We pause in our hurried flight across the Mexican _bajadas_, as a strange and lurid spectacle comes into view. It is a forest of the Giant Visnaga, greenish monsters of the desert, appearing to rise out of the ground in front of us, towering on their fantastic yellow-green bodies and leaning toward us, like some strange messengers of a departed world come back to us in this graveyard of the desert. The Giant Barrel is the cactus in search of which we have traveled all the way from Southern California to San Luis Potosí, in Central Mexico, a monster growth six to nine feet tall, three to four feet in diameter, weighing over four thousand pounds; and estimated by scientists to attain the age of a thousand years! One of these Giant Bisnaga has been growing in the University of Arizona gardens for thirty-five years, is only about two feet tall and eighteen inches through, even after the lapse of a third of a century. It is in the highlands of San Luis Potosí that we have discovered this giant, just as our long hot trek is drawing to a close. We see that his trunk is single and unbranched, cylindrical, and greenish or yellow-green. The four straight sharp stout thorns are all brownish central spines; no radials are present. The flowers are bright yellow and showy, and the tops of the plants where they appear are covered with dense layers of long woolly cream-yellow hairs. The large blossoms, two and one-half inches long and as broad, come forth in early June, spreading wide open in the forenoon and closing in late afternoon. Whipple’s Visnagita (_Echinocactus Whipplei_) _Northern Arizona, Northern Utah, Western Colorado, and New Mexico_