Contrasting the plants of this region with those of the European Alps it is interesting to note, that while the species are for the most part vastly different, yet there is a certain close resemblance in the families and genera which are represented; the Anemones are here, but not in the scarlets and crimsons, running more to whites and purples, and so are the Buttercups, dwarf many of them, but with large, showy flowers; the Saxifrages and Drabas are innumerable as are the Vetches and also the Heaths, but the latter with fewer and very different species. Some plants, however, like the White Mountain Avens (_Dryas octopetala_), the Butterwort (_Pinguicula vulgaris_), the Moss Campion (_Silene acaulis_), the Mountain Cranberry (_Vitis-idæa_) and the Low Cranberry (_Oxycoccus_), the One-flowered Wintergreen (_Moneses uniflora_), the Forget-me-not (_Myosotis alpestris_) and others are found on both sides of the Atlantic, yet we have no such array of Primroses or Gentians as our European brothers, though both genera are represented with us, while on the other hand they can boast of nothing comparable to our Indian Paint-Brush, found throughout the region on the river shores and bars during late June and early July and later through the summer in its innumerable forms and colours in the moist alpine meadows and slopes. The ferns and their allies with the more striking of the trees and shrubs have been included in the present work, together with the majority of the herbaceous flowering plants, though some of the largely represented but less striking groups such as the Grasses, Sedges, and Willows have been entirely omitted, not seeming of sufficient general interest to warrant the space required for their intelligent treatment. The species are arranged in accordance with their scientific relationships, with keys to the genera and a general key to the families. Among the illustrations herein contained, many of the plants of the Northwest are figured for the first time. Acknowledgment is here made to Messrs. David McNicoll, Robert Kerr, and other officials and employees of the Canadian Pacific Railway Company through whose courtesy was made possible the gathering of the data for the basis of this work. S. B. ACADEMY OF NATURAL SCIENCES, PHILADELPHIA, October 28, 1907. CONTENTS