658 Part IV. Chapter 6. 
rivers are marked by Tarodium mucronatum and in deep barrancas by this 
tree and immense wild fig trees. The hills about Lake Patzcuaro are pine 
clad with oak and pine reaching to the mountain summits beyond, comprising 
a Forest Formation of such trees as Pinus Montezumae, Quercus reticulata, 
O. undulata and Arbutus varians. On the ridges near Guadalajara are found 
Pinus oocarpa and Quercus fulva. Vigna strobilophora is a twining vine with 
a woody stem climbing to the tops of shrubs and low trees, while Vzrex pyra- 
midata is a small spreading tree found on rocky bluffs above Tequila‘). Zrzo- 
dendron tomentosum is a large tree which occupies the warmest barrancas. 
The tropie portions of southern Michoacan is a mountainous area with scattered plains here 
and there. The plains are grass covered with irregular patches of scrubby trees and shrubs 
about their borders with a singular species of Agave on the bare sunbaked cliffs of canyons. The » 
chaparral formation of this coast is found in the valley of the Balsas River and elsewhere. 
Here is found an abundant growth of various kinds of large cactuses, thorny shrubs and low trees 
which extend down to this coast. Near Acapulco are bold and rugged headlands with many 
large cactuses on their seaward faces). 
The lagoons of the Jaliscan coast are characterized by the mangrove tree, Rhizophora 
mangle and associated species, but the absence of details precludes a more careful statement of 
floristice conditions. 
2. Gulf Region. 
The Gulf Region of Mexico comprises three distinct classes of formations: 
the coast littoral formations, the chaparral formations and the tropic forest 
formations. 
Littoral Formations. Here we have ocean emibayiienis characterized 
by such sea weeds as Padina pavonia, Dictyota spec., Nemalion, Halimeda 
Opuntia and Sargassum Montagnei;, species which are usually Ol in shallow 
water with a bottom of calcareous sand °). 
According to my observations made at Tampico on the Gulf coast of 
Mexico, the sand-dune formation conforms to that of the American tropics 
in general. /fomoea pes-caprae is the characteristic plant of the low dunes of 
his sandy coast trailing down upon the upper beach. Dunes occur along the 
north coast of Yucatan. Here occur Bravaisia tubi ıflora, Croton punctatus and 
in the shade of bushes Beloperone violacea, Dicliptera assurgens and eier: 
heterophylla*). 
The Mangrove Formation is confined to lagoons which are formed primarily by a bar 
of sand forming across the mouth of some river. Rhizophora Mangle, Avicennia tomen- 
tosa and related species constitute the plants of this formation which extends in favorable places 
along the entire Gulf coast of Mexico and north coast of Yucatan, where Rhizophora, Coccoloba 
1) PRINGLE, C. G.: Notes on Mexican Travel in Michoacan. Garden and Forest VI. 263; 
in Jalisco VII. 152. 
) NELsoNn, E. W.: A winter Expedition in southwestern Mexico, National Geographic 
Magazine XV: 341—356. Sept. 1904. 
3) VILLAGOMEZ, IGn. OCHOA: Vera Cruz. 1885: see Bibliogr. p. 87. 
4) SELER, Ep.: Zwei Frühlingsmonate in Yucatan. Festschr. zum us Geburtstage ASCHERSONS 
1904: 371—382. 
