In the matter of generic delimitation we are in still greater uncertainty, and several generic lines at present recognized must be regarded as purely arbitrary, a fact which must become still more evident with additional material. The whole group is to be regarded as made up of poorly differentiated forms and only long observation under cultivation can determine the possibilities of specific variation under the influence of environment, of age, of inherent tendencies. For instance, that these plants change in form and in spine characters with increasing age and after they have begun to flower can not be doubted, but what described forms have thus been separated in descriptions can only be guessed at. John M. Coulter. Lake Forest University, Lake Forest, Ill., January, 1891. CACTUS, ANHALONIUM, AND LOPHOPHORA. 1. CACTUS Linn. Sp. Pl. 466 (1753), restricted. MAMILLARIA Haw. Synop. 177 (1812), not Stackh. (1809). Usually globose to oblong plants (simple, branching or cespitose), but sometimes slender-cylindrical, covered with spine-bearing tubercles: flower-bearing areola axillary (with reference to tubercles), entirely separate from the terminal spine-bearing areola, although sometimes (Coryphantha) connected with it by a woolly groove along the upper face of the tubercle: ovary naked: seeds smooth or pitted: embryo usually straight, with short cotyledons. Originally defined by Linnaeus in his Systema, ed. l (1735). The Linnaean genus Cactus of 1753 included 22 species and was coextensive with the present order. In 1812 the species were separated by Haworth into five genera, the original generic name Cactus being discarded. Among these species C. mamillaris seems to have stood as the type, not only of the Linnaean genus Cactus, but also of Haworth's Mamillaria, and as such should retain the original generic name. Besides, Mamillaria was used as the generic name of an alga in 1809. Cactus mamillaris L. is the West Indian Mamillaria simplex Haw. From one point of view the two sections of the genus (Eumamillaria and Coryphantha) deserve generic separation, for the character of grooveless and grooved tubercles seems to hold without exception, and the sections are separated with more certainty than are certain species of Coryphantha and Echinocactus. If genera are simply groups of convenience the separation should be made. I. EUMAMILLARIA. Flowers from the axils of the older or full-grown tubercles (hence usually appearing lateral), mostly small, and generally from whitish to pink or red: tubercles never grooved: fruit almost always clavate and scarlet. A. Tubercles more or less quadrangular. * Central spines not hooked. + More than one central spine. 1. Cactus alternatus, sp. nov.