Tropie Zone: Gulf Region. 659 
and such halophytes as Batis maritima, Lithophila vermiculata (= Gomphrena vermicularis) and 
Heliotropium curassavicum occur. — 
The species of aquatic plants which exist in the lagoons (such as Tamulte and Ocuiltza- 
potlan) either submerged or floating are Vallisneria spiralis, Cabomba aquatica, Ceratophyllum, 
Potamogeton, Heteranthera graminea, Limnanthemum Humboldtianum, Villarsia Humboldtiana, 
Marsilia polycarpa, Nymphaea ampla, Eichhornia azurea, Pistia stratiotes, Jussiaea natans, Neptunia 
oleracea, Azolla caroliniana?). — The marshes, near such lagoons, are characterized by Typha 
angustifolia, Acrostichum aureum, Ceratopteris thalietroides, Thalia genieulata, Cyperus articulatus, 
Arundo and in salt marshes Scirpus maritimus. — e lagoons or morasses are distributed 
in Tabasco in all situations where depressions of the earth exist. These are frequently dry during 
the months of March, April and May. It is evident that this change influences the vegetation 
and in addition to the floating and submerged species, the botanist notes in such dry morasses 
Lonchocarpus hondurensis, Haematoxylon campechianum, Inga spuria, Dalbergia campechiana, etc. 
Chaparral Formation. The chaparral formation extends into southeastern 
Texas where the character of the vegetation is controlled by a minimum of 
-rainfall, a dry air subject to regularly recurring movements of great velocity 
and a high percentage of days of intense sunshine related to edaphic factors 
in which the soil has the loose, shifting, incohesive quality formed by 
dry weathering and destitute of vegetal mould, if not gravelly, or stony, and 
where the soil water level is too deep to be available for any but perennial 
plants with far reaching roots. The chaparral is typically a low, more or less 
impenetrable bush covering continuously vast areas, and varying in height from 
two or three feet to ten or fifteen, according to the ecologic conditions. In 
the lower Rio Grande country, the chaparral is rapidly encroaching on the 
prairie formations which were formerly more extensive’). 
On the basis of temperature, there is a distinction of species into those of 
semitropic and even tropic affınities and those able to endure the freezing 
winter temperatures of the warm temperate zone. The former occur chiefly 
in the lower Rio Grande country, the latter constitute, the chaparral of the 
northern half of the plain, spreading also by some species into central Texas. 
Geologic structure and conditions of soil, according to BRAY?), act powerfully 
to determine the facies of the formation upon any given area. Thus, gravelly 
slopes, denuded of finer sediment, may have a pure facies of straggling. 
Parkinsonia texana, and basalt ridges are thickly covered by a short bushy 
facies of Acacia Berlandieri. It is noticeable that no less than 30 per cent 
of the number of species and a far higher percentage of actual individuals 
belonging to the leguminous suborders Mimoseae and Caesalpineae. The Gulf 
Strip of Texas is approximately indicated by the range of Acacia farnesıana 
and Parkinsonia aculeata, both of these of tropic range. 
Lantana camara, 
BAILEY adds to these Daubentonia longifolia (= Sesbania Cavanillesii), 
elegans, Yucca 
Amyris parvifolia, Karwinskia Humboldtiana, Maximowiezia Lindheimeri, Nymphaea 
nn 
1) Ramirez, Dr. Jos: see Bibliography p. 85. ei 
2) Brav, WiLLıam, L.: Forest Resources of Texas, p. 33: se® Bibliogr. P- 75: 
3) Brav, W. L.: Botanical Gazette XXXIL 270—274: see Bibliogr. P. 75. 
42* 
