United Cordilleran Region. 651 
islands were noticed Sagittaria sagittifolia var. mexicana, Cyperus unioloides, Eriocaulon Benthamii, 
Polygonum amphibium, Lobelia fulgens, Solidago panieulata, Cnicus linearifolius, Bidens chrys- 
anthemoides and in the ditches Ranunculus cymbalaria, R. orthorhynchus and a species of 
Arundo, etc. In Lake Lerma in the valley of Toluca grows Nymphaea gracilis. 
Dry Ridge- and Pedregal-Formation. The dry hills in the valley of 
Mexico support a scant vegetation. On the Cerro de Guadalupe, connected 
with the western mountain chain by a low ridge, Cuesta de Barrientos, I noted 
Milla biflora (on exposed rocks), Talinum aurantiacum (on rock faces), T. patens '), 
Oxalis decaphylla, Mamillaria strobiliformis, Tecoma mollis. 
The pedregal, or lava bed was formed by streams of lava that flowed 
from Serrania de Ajusco down through a distance of twenty-five miles over 
nearly all the mountain side and over the southern edge of the Valley of 
Mexico. It consists of sharp ridges alternating with deep crevasses. 
Doubtless, it was once covered with a scanty forest growth, because on the 
mountain side at 8—10,000 feet, I noted groves of Pinus leiophylla associated 
with Oxercus reticulata, O. undulata and beneath these trees three species of 
Dahlia (D. Merckü, D. coccinea, D.variabilis) with masses upon masses of 
conspicuous bloom, Cranothus azureus, Lupinus silvaticus, Physalis pubescens 
and parasitic upon the oak roots Conopholis mexicana, while Agave megalacantha 
is dotted here and there among the other plants. In the pockets in the lava 
rock occurs between many herbs the curious, composite, woody plant, Senecio 
praecox with water storing stems?). Selaginella lepidophylla (a resurrection 
plant) is abundant on the faces of the lava ridges, associated with Nofholaena 
Ferruginea, Cheilanthes myriophylla, Pellaea gracilis. Several grasses also are 
abundant: Bouteloua prostrata, Microchloa setacea and a sedge, Cyperus Ses- 
leroides. — The lava beds (pedregal) at a still higher elevation, 11,000 feet 
on the Sierra del Ajusco, are characterized by Fumperus tetragona, Pinus 
Montezumae, associated with smaller plants, growing out of the soil-filled 
pockets in the lava. 
2; Forests and Mountain Meadows. 
Coniferous Forest Formation. The pine belt is typically developed on the 
- hylla which grows 
Sierra del Ajusco between 8,000 and 11,000 feet. Pinus leiop 
in pure forests at about 9,000 feet is replaced higher up by Pinus Me 
On the slopes of the mountains above the valley of Toluca, this pine an 
en unidentified pine form almost pure forests. 
the fringe to the forest and the cool wet ravines are 
ee of Adies religiosa. This sub - alpine mountain. tree a ne 
Abies religiosa Belt with at times Pinus Montezumae intermixed. 
undergrowth consists of Alnus acuminatus, 
alinum: see Bibliogr. P- 83 
)H : sT nn : 
I a er Senecio praecox: See Bibliogr. P- 83; Mac 
2) HARSHBERGER, Jonn, W.: Water’ Storage in 
Dovsar, D. T.: The Pedregal. The Plant World X: 285. 
