extensive and vitally important place in the economy of Nature. Of these last few one instance rises up most prominently of all, certainly without a full parallel elsewhere in the field of botanical science—and do we realize that it stands almost at our doors? It is the great three-typed plant group that forms the major part of
Fig. 2.—Cereus Triangularis.
the flora of the far Southwest, on the arid plateaus and plains and rocky mountain heights of Arizona and New Mexico, western Texas and southernmost California, and over the boundary line far into northern Mexico. Here is the fatherland and here the supreme province of those three marvels of plant life—the cacti, with their strangely specialized vegetative body; the agaves, to which popular tradition has attached an epithet of fitting dignity in the name of "century plants"; and, thirdly, the yuccas, which claim, in addition to their floral splendor, the distinction of manifesting the interdependence of the flower and insect worlds with
