doubtless, also, Melocactus, seeds of which, however, have not been examined by me; and Echinocactus, mostly with a curved embryo. The second class includes Echinocereus, with a nearly straight embryo, and very short cotyledons; Cereus, with a curved embryo, and foliaceous incumbent cotyledons, (probably also Echinopsis and Pilocereus, and perhaps Phyllocactus and Epiphyllum;) Opuntia, with a circular or spiral embryo, (circular and with a larger albumen in all Opuntiae cylindraceae; spiral and with a much smaller albumen in all Opuntiae ellipticae, examined by me,) and very large cotyledons. Rhipsalis and Pereskia may also belong here, but were out of my reach.
The flowers of all the species belonging to the first class, with the doubtful exception of some Mammillariae, make their appearance on the growth of the same year. Those of the second class produce the flowers always upon the growth of the next preceding or former years. The first class may, therefore, be distinguished by the name of Cactaceae parallelae, (from the direction of the cotyledons,) or C. apici florae, (from the position of the flowers.) The second class can be named, in a corresponding manner, Cactaceae contrariae, or C. lateriflorae.
Echinocereus is principally distinguished from Cereus proper by its low growth; its short, more or less oval stems, which are frequently branching at base, and thereby cespitose; by the diurnal flowers, with short tubes; by the nearly straight embryo, with short cotyledons. From Echinopsis, to which some species have been referred, it differs also by the short-tubed diurnal flowers, and by the numerous filaments being adnate to the lower part of the tube. For further particulars compare the note 7. The species of Echinocereus inhabit Texas and the northern parts of Mexico, where Cerei proper are very rare. They extend even farther north than the Echinocacti, but appear to be excluded from the old limits of the United States, where the cactus family is represented only by some Opuntiae and Mammillariae. The southern limits of the Echinocerei are unknown to me, but I doubt whether they extend far in that direction; the nearly-related Echinopses, on the contrary, appear to be exclusively inhabitants of South America, especially the La Plata countries.
As I am speaking of the geographical distribution of the Cactaceae, I may as well add here that Mammillariae were found throughout the whole extent of Dr. Wislizenus’s tour, and that at least four species occur in Texas. Echinocacti were observed only south of Santa Fe, and from there to Matamoros, but none on the highest mountains, which were occupied by the Opuntiae, Mammillariae, and Echinocerei; two Echinocacti have been found in Texas. Only two species of true Cerei were seen; one of a peculiar type about Chihuahua, and another near the mouth of the Rio Grande, which does not appear to differ from the wide-spread C. variabilis, Pfeiff. Opuntiae ellipticae, as well as cylindraceae, were observed from New Mexico to Matamoros, and species of both are also found in Texas. Melocacti, Phyllocacti, and other genera of Cactaceae, not mentioned above, were not met with.
The notes and collections of Dr. Wislizenus confirm the opinion of that acute observer and successful cultivator of Cactaceae, Prince Salm-Dyck, viz: that most species of this family have a very limited geographical range, the most striking exception being those belonging to the genus Opuntia.
