16 BOTANY. 



surface being, however, covered with thickets of Ceanothus, Purshia, Spircea, Amelanchier, 



Cercis, Fremontia, Manzanita, a low scrub oak, (undescribed,) and a wild plum, (P. subcordata.) 



At an altitude of about 3,000 feet we entered a dense forest composed — with the exception of a 



single oak, (Q. Eelloggi,) — of coniferous trees, the sugar and yellow pine, Libocedrus, and balsam 



fir, all attaining a very large size. At MeCumber's, at an elevation of 4,000 feet, the forest 



was composed exclusively of coniferous trees, and was, in many places, very dense. The 



natural meadows, of which MeCumber's flat is one, are covered with a luxuriant growth of 



annual plants, of which I collected nearly a hundred species in a few hours. As a whole, 



however, the catalogue does not differ greatly from one which might be made at Fort Beading, 



or in Sacramento valley, earlier in the season ; but while, at this time, (July 29,) the plains of 



the Sacramento were completely dry, and the flowers of spring had long since passed, here 



everything was fresh and green, and the meadows were decked with flowers at the period of 



their greatest beauty. In the pine forest, the snow berry, (Symphoricarpus,) Rubus nutkanus, 



(a variety of R. odoratus ?) and Epilobium angustifolium, grow everywhere, and the ground is 



in many places covered with mats of Ceanothus prostratus. Lillies and fritillarias also form a 



marked feature of the pine woods here as elsewhere. As we ascended to the summit of the 



pass, at an altitude of about 5,000 feet, we left behind us most of the trees which I have 



mentioned, and found the forest of the higher portion of our route composed exclusively of the 



yellow pine. About the base of Lassen's butte, where, over a large area, the forest had been 



burned off, it has been succeeded by dense thickets of Ceanothus and Manzanita, and along the 



banks of a stream coming down from the snow I noticed a Cornus, having much the general 



aspect of C. Florida, of the eastern States, but evidently quite distinct, (C. pubescens.) On the 



eastern slope of Sierra Nevada we found the forests much less dense, and composed of a 



smaller number of elements. The yellow pine here formed nine-tenths of all the arborescent 



vegetation, and grows to a larger size than on the western side of the mountains. This slope 



is evidently not so well watered as the other, and even among the mountains, in various 



localities, we found level surfaces, of which the light volcanic soil supported only bunches of 



Artemisia and Purshia, with scattered yellow pine trees, outliers of the sage plains, so 



characteristic a feature of the region lying east of the mountains. 



BOTANY OF THE DISTBICT LYING EAST OF THE SIEBBA NEVADA AND 



CASCADE MOUNTAINS. 



Descending to the eastward from the summit of the western range of the Sierra Nevada, we 

 came into a region of which the geological structure and physical features are fully described in 

 the geological report. The general monotony of the geological structure of this area finds a 

 perfect parallel in the simplicity and uniformity of its vegetation. Throughout all the interval 

 lying between the Cascades and Sierra Nevada and the Bocky mountains, the causes which 

 have given character to the vegetation have been exceedingly general in their action. The 

 climate is everywhere characterized by the absence of moisture, which, with the exception of 

 the mountain summits, which project above the general level, gives to the surface a character to 

 which the name of desert has not been inappropriately applied. The general aspect of the botany 

 of this region is made up of three distinct elements. Of these the first is presented by the grassy 

 plains which border the streams flowing down from the mountains. On these surfaces grows a 

 considerable variety of annual vegetation, in its general character not unlike that of the Sacra- 

 mento valley. The second of these botanical phases is that of the sage plains ; surfaces upon 



