VEGETATION OF THE SANTA CATALINA MOUNTAINS. 33 
The pure or nearly pure stands of Pinus arizonica which occur be- 
tween 8,000 and 9,000 feet are increasingly poor in the evergreen oak 
shrubs, which have disappeared at the latter altitude. The clumps of 
young Quercus submollis give the forest its only deciduous element at 
this altitude, and the low patches of Ceanothus, so common at 8,000 
feet, give way at 9,000 feet to Symphoricarpos oreophilus and to the 
much less frequent Holodiscus dumosus. Very many of the commonest 
herbaceous perennials of the Pine Forests which lie between 7,000 and 
8,000 feet do not reach 9,000 feet, or are replaced in the physiognomy 
of the forest by closely related species. On the summit and southern 
slopes of Mount Lemmon the commonest herbaceous plants are: 
Keleria cristata, Dugaldia hoopesii, Erigeron neomexicanum, Pteris 
aquilina var. pubescens, Gnaphalium decurrens, Hieractum lemmoni, 
Senecio sp., Aniennaria marginata, Silene greggit, and Helianthella 
arizonica. Throughout the higher Pine Forest Arceuthobium diwari- 
catum and Arceuthobium robustum are common on the trunks and limbs 
of Pinus arizonica. 
At about 6,800 feet Alnus acuminata, Acer interior, and Quercus 
submollis become frequent along streams (see plates 30 and 31). The 
first two are confined to this habitat throughout their vertical range, 
while the oak, which is the only deciduous member of the genus in 
these mountains, is found even in some of the driest situations above 
7,600 feet. Quercus submollis occurs characteristically either as single 
trees of considerable size, up to 40 feet in height and 4 feet in girth, 
or else as crowded circumscribed groups of young trees, which doubt- 
less owe their juxtaposition to the accidents of seed dispersal. Salix 
taxifolia is also a common streamside shrub above 6,800 feet, and 
in certain portions of the mountain Rosa fendleri is abundant in the 
proximity of streams. 
Herbaceous plants are to be found in increasing numbers at or near 
the banks of streams between 6,000 and 7,400 feet. Prominent among 
them are: Juncus arizonicus, Aquilegia chrysantha, Thalictrum fendlert 
var. wrightti, Scrophularia sp., Trifolium pinetorum, Fragaria ovalis, 
Potentilla thurberi, Hypericum formosum, Lobelia gruina, Agrimonia 
brittoniana var. occidentalis, Gaura suffulta, and Tagetes lemmont. 
THE FIR FOREST. 
Between 7,000 and 7,400 feet is a rapid change in the character of 
the forest stands on northerly slopes, due to the increasing occurrence 
of Pseudotsuga mucronata and Pinus strobiformis, the lower limits of 
which have already been mentioned, and to the appearance of Abies 
concolor. These three species occur in mixed stands together with 
Pinus arizonica on northerly slopes up to about 7,500 feet, above which 
elevation the latter becomes a very infrequent tree on slopes facing 
directly north, although it still occurs in admixture with Pseudotsuga 
