United Cordilleran Region. 653 
by the fields of ash and scoria which prohibit the growth of pine species, and not by the abso- 
lute amount of temperature which is peculiar to each species of tree, The plants of these pine 
woods are Ranunculus geoides (11,000 feet), Cerastium orithales (13,000 feet), C. vulcanic 
(11,000 feet), Sambucus mexicana (10,000 feet, Arracacia nudicaulis (12,000 feet), Tillandsia punctu- 
lata (10,000 feet)2), compare the observations of LiEBMANN, made in 1844: At 10,000 feet 
(3,360 meters) with Pinus teoeote in addition to the above occur Pirola rotundifolia, Chimaphila 
maculata, Woodwardia ciliata (= Cheilanthes marginata), Acrostichum Schiedei (= A. rubiginosum) 
and A. simplex and certain arborescent Ericaceae: Arbutus floribunda, A. laurina, A. paniculata, 
A. Menziesii. 
The following plant grows on the dry rocky walls: Echeveria (Cotyledon) mucronata 
and ferns of the genera Asplenium, Nephrodium (Aspidium, Dryopteris), Notholaena, Adiantum, 
Cheilanthes, Polypodium together with species of Pinguicula, Stevia, Senecio, Baccharis and Vale- 
riana plantaginea. 
n the upper timber belt are found Pinus strobiformis (= Ayacahuite) and P. Hart- 
wegii, which range to about 14,000 feet and perhaps two to three hundred feet higher on the 
adjacent Sierra Negra. At 13,200 feet, these trees form groves, or thickets, 30—40 nn high. 
The belt of the Mexican mountain fir, Abies religiosa, on this mountain ceases at an eleyation of 
11,500—12,000 feet. Juniperus tetragona covers the bare rocks of Mount Orizaba at some little 
distance beyond the actual tree line. On such rocks above tree line, according to LIEBMANN (loc. 
eit.), are found mosses and lichens of the genera Bartramia, Pohlia, Lecidea, Bryum, Didymodon, 
Trichostomum and Stereocaulon. 
Alpine Formation. At about 12,000 feet, where the exposure and slope 
is such as to inhibit the growth of trees, for example, along the edges of 
barrancas, occur grassy stretches characterized by Pedicularss ae 
Eryngium proteaeflorum, Stenanthium frigidum, Cerastium vulcanicum = 
orithales, Arenaria leptophylla, Ranunculus geoides, Nasturtium orizabae, Draba 
tolucensis, Stevia purpurea and arbutifola, while along the courses of moun- 
tain rivulets occur species of Carex Barbarea, Funcus, Luzula Be Above 
13,600 feet, the grass belt becomes the feature of the mountain Fe 
to snow line. A number of plants disappear at the lower edge of this belt, 
viz., Acaena elongata, Poa annua and Bryum Bpeheiin 3m ] a 
covering consists of Festuca tolucensis and lwida, Ti dig z =. na 
Deyeuxia recta, Epicampes macroura (= CryPs? stricta), many ha Dale 
Festuca-species. Here exists an Andean genus of Ericaceae (see ante p. 302) 
Pernettya ciliaris, on dry sandy soil. 
e marshy places formed by the melting SE DEN we il olor associated 
reniformis which with a species of Potentilla renders such areas of a yellow x 
with Phleum Haenkeanum (= P. alpinum) and species of Veronica, A 
: z tee d Juniperus tetragona, 
e rocky aiguilles are covered with Berberis (Mahonia) ilicina an 2 Be nie 
vellea (13,000—14,000 feet), U. eylindrica and U. proboseidea i d elumps in serried 
At this elevation, the landscape is forbidding, for the grasses st 
tows with the light loosely compacted volcanie ash 
Covering all the vegetation with a grayish mantle. Here and the a 
the scene is relieved by some projecting rock mass, te ‚vegan * 
described 
re, however, - 
hich has just been 
# R ‘hli hy p- 86. 
I) SEATON, HENRY, E.: Plants collected on M. Orizaba 1891: see Bibliography 
