Page:Memoir of a tour to northern Mexico.djvu/91

Rh base, while most other Gerania have them united for about two-thirds or more of their length.

In the prairies about Wolf creek, in an elevation of between 6,000 and 7,000 feet, the smallest of a tribe of cactaceæ was discovered, numerous species of which were found in the course of the journey south and south-east: several others have also been discovered in Texas. I mean those dwarfish Cerei, some of which have been described with the South American genus Echinopsis, or have been referred alternately to Cereus or Echinocactus, and which I propose to distinguish from all these under the name of Echinocereus, indicating their intermediate position between Cereus and Echinocactus: they approach more closely to Cereus, in which genus they, as well as the genus Echinopsis, should perhaps be included as sub-genera.

The species mentioned above is distinguished from all others known to me by its yellowish green flowers, the others having crimson or purple flowers. I have named it, therefore, Echinocereus viridiflorus.

A careful examination of the seeds of numerous cactaceaecactaceæ [sic], has indicated to me two principal divisions in that family: 1. Cotyledons, more or less distinct, directed with their edges to the edge, (or towards the umbilicus,) and with their faces to the flattened side of the seed; when curved, accumbent. 2. Cotyledons, mostly very distinct, foliaceous, direct with their edges to the faces, and with their faces to the edges of the seed, (or towards the umbilicus;) when curved, incumbent, and often circular or spiral.

The first class comprises Mammillaria, with a straight embryo; and