Page:Memoir of a tour to northern Mexico.djvu/112

[ 26 ] collected thriving plant and flowers, and Dr. Gregg the ripe fruit. It is distinct from the other Echinocacti found in those regions by the membranaceous very thin sepaloid scales on the tube of the flower and the juicy glabrous fruit, in which respect it resembles my E. setispinus from Texas; E. texensis, Hpfr., has a juicy fruit, covered with woolly and spiny scales; E. Wislizeni and others have a dry fruit, covered with hard scales.

My Opuntia frutescens (Plant. Lindh. 1. c. p. 245) which had been collected by Mr. Lindheimer along the Colorado and Guadaloupe rivers, in Texas, was also found south of Chihuahua by Dr. Wislizenus, and again along the route near Parras, and below Monterey. The suggestion made in the Plant. Lindh., that it may be a southern variety of O. fragilis of the Upper Missouri, has proved to be erroneous, as they belong to quite distinct sections of the genus Opuntia; O. frutescens, together with O. vaginata, (vide note 18,) is one of the Opimtiae cylindraceae graciliores, and is apparently nearly related to O. leptocaulis DC, but is easily distinguished by its strong, white, single spines, while O. lept. has 3 short blackish bristles.

Agave Americana, with several relatives, was found in abundance on this part of the route; Argemone Mexicana, white, yellow, or rosecolored, was frequently met with; Samolus ebracteatus occurred in moist places so far inland, and on such elevations, while before it was only known as a litoral plant; Malvaceae, Oenotherae, Asclepiadaceae, Giliae, Solaneae, Justiciae, shrubby Labiatae, were collected of many different species; but the great characteristic of the country were the shrubs forming the often impenetrable thickets, called "chaparrals." They are mostly spinous,