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[ 26 ] by Dr. W. arrived here in the best condition, and some have already germinated, so that we may hope to raise some of these species. Yucca aloëfolia, of the southern United States and Mexico, is said also to bear an edible fruit, but has serrulate leaves; we have, therefore, different species of Yucca with edible fruits, which may constitute a peculiar section in this genus.

The soil appeared to be too fertile here for the production of Cacti; and with the exception of some Opuntiae, the only species collected between Paso and Chihuahua, about 100 miles south of the former place, was Cereus Greggii which was peculiarly interesting, as it is probably the most northern form of Cereus proper. The specimens sent for cultivation by Dr. W. were unfortunately dead when they arrived here, and neither flower nor fruit had been obtained; but Dr. Gregg has collected the same species near Cadena, south of Chihuahua, in flower, from which I completed the description. I could not have given it a more appropriate name than that of the zealous and intelligent explorer of those far off regions, learn from Prince Salm-Dyck that a Cereus, probably the same species., was sent to England by Mr. Potts, of Chihuahua, but his specimens also did not live; they were very remarkable for having a thick turnip-shaped root. Neither Dr. W. nor Dr. G. having paid attention to the root, I am unable to say whether their specimens agreed with those of Mr. Potts in this particular.

Dr. Wislizenus was forced to go from Chihuahua westward to Cosihuiriachi. However prejudicial this involuntary interruption of his journey may have been to the primary objects of his expedition, it appears that he could not have selected a more favorable field for botanical researches. Amongst the porphyry mountains of Cosihuiriachi and Llanos, which vary from 6,000 to 8.000 feet in height, and their deep chasm-like valleys. a great many undescribed species of plants were found; in fact almost everything collected there appears to be new!

Among the trees, I mention three species of pines, entirely different from those found farther north, but perhaps identical with some species from the Pacific coast. The most magnificent of these three is a species nearly related to Pinup strobus and Pinus flexilis, which I name P. strobiformis. Its size and growth, its foliage, as well as the shape of the