654 Part IV. Chapter 5. 
The herbaceous plants which extend their growth to an elevation of 12,000 to 
15,000 feet on Mount Orizaba are, according to HeitLprin?): Ranunculus peruvianus, Draba 
myosotidioides, Arenaria bryoides, Potentilla Richardii, Heuchera orizabensis, Peucedanum tolu- 
cense, Senecio chrysactis, S. multidentatus, S. orizabensis, Hieracium niveopappum, Lobelia nana, 
ee pungens, -Phacelia pimpinelloides, Mimulus glabratus, Spiranthes ochracea and Ste- 
he 
anthium frigiddum. The herbs that reach an elevation between 13,000 and 15,000 feet on 
Ciba are: Draba tolucensis, Arenaria bryoides, Acaena elongata, Ribes jorullensis, Stevia arbu- 
tifolium, Senecio cirsoides (= S. roseus), S. gerberaefolius, S. procumbens, Cnicus ee Per- 
ur ciliaris, Veronica er, Castilleja tolucensis. The last plant to disappear on Ori- 
a peak is Castilleja tolucensis and a Dr aba (D. aretoides, or D. popocntepelens both 
of which, according to HEILPRIN, die close to snow line, or nearly to 15,000 feet. On the 
blocks of rock above 14,600 feet where, according to Fe the last flowering plant occurs, 
grow a lichen, Rhizocarpon (Lecidea), geographicum and a moss Grimmia apiculata, while here 
also occur Tortula ruralis, Parmelia Ehrhartii, Lecidea en L. vitrina and above all these, 
as the last plant, Parmelia elegans. 
Popocatepetl. The belt of cactus, nopal, mesquite of the Mexican plateau 
is replaced higher up on Mount Besnstepell by a belt of pines (Coniferous 
Forest Formation) consisting of Pinus Montezumae, Pinus Teocote and P. 
pseudostrobus at an elevation above 9,000 feet. These long-leaved pines are 
replaced by short leaved pines. Pinus strobiformis and P. Hartwegüi which 
reach to approximately 13,000 feet, (13,160, according to HEILPRIN), the trees 
being of inconsiderable heights. Zupinus vaginatus extends to 13,000 feet. 
Senecio chrysactis reaches the limit of the pines on all of the loftiest mountain 
summits forming with the lupine a compact undergrowth to the pines, especi- 
ally where the latter have been thinned into groves leaving patches of open 
country in their midst. ‘Here the vegetation is most luxuriant and the eye 
revels in the brilliancy of colors which are everywhere manifest. 
Alpine Formation. Beyond the limit of trees (above 13,000 feet), the vegetation con- 
tinues over the slopes as a long wiry grass to a point 500 feet higher?), although the sands 
blown about by the winds frequently cover the grass and choke it. The grasses which occur 
above timber line (13,000 feet) are: Sporobolus Wolfii (just below timber line under the pine 
trees, Pinus Hartwegii), . mucronata, Muhlenbergia quadridentata, Cinna (Deyeuxia) tolucensis, 
Trisetum Rosei var. ten ‚ Trisetum er Poa conglomerata, Poa infirma, Festuca amplis- 
sima, F. aequipaleata, F. ri The last grass and Trisetum Rosei were found by RosE3) asso- 
ciated together at 13,400 feet, Telketun Rosei was found alone at 13,500 feet, the exact alti- 
tude at which Festuca livida was found on Mount Orizaba. This grass, therefore, holds the 
distinction of growing at a higher altitude than any other flowering plant on the North 
American continent, except Festuca livida. Both grow in and under the melting snow, 
pushing up along the tongues of sand, soon to be buried under a fresh fall of snow. 
Ixtaccihuatl. The flora of this mountain is richer than that of Popoca- 
tepetl, according to Sonntag and Farrington. The succession of forest belts 
1) HEILPRIN, A.: The temperate and alpine Floras ete.: see Bibliogr. p. 83; C „A.R.: 
An Ascent of Mt. Orizaba. Pop. Sci. Month. 1902: 528—535; GAapow, Hans: rei nr 
Mexico 1908: 41— 72 (Orizaba), 487—499 (Popocatepetl); see ante page 302. 
2) FARRINGTON, O. C.: Popocatepetl and Ixtaccihuatl: see Bibliogr. p. 83. 
3) Rose, J. N.: Studies No. 4. 1905. 287—290: see Bibliogr. p. 85. 
