Mangrove — Chaparral — Tropie Forest. 301 
Chaparral Vegetation. A chaparral region occupies the coastal plain in 
eastern Mexico above which the rain clouds sail high and it is, therefore, rather 
arid. This chaparral strip expands above Tampico and comprehends the 
valley of the lower Rio Grande River and all of that portion of southern Texas 
below a line which stretches from Eagle Pass on the Rio Grande through San 
Antonio, Texas to the coast. No fewer than forty species, according to Bray ‘), 
associate in this formation in many cases a limited area is tolerably uniformly 
covered by at least half of all the species and sometimes a single species 
constitutes almost the entire formation over extensive tracts. There is a 
distinction of species into those of semitropic and even tropic affınities and 
those able to endure the freezing winter temperatures ot the warm temperate 
zone. The prevalence of Mimoseae and Caesalpinieae in the Rio Grande 
chaparral deserves special mention. No less than 30 per cent of the number 
of species and a far higher per cent of actual individuals represent the strength 
of these elements in the formation. This also emphasizes the semitropic af- 
finities of the flora and there cannot be, therefore, any doubt but what the Rio 
Grande chaparral represents a northern extension of the one found extending 
southward on the eastern coastal plain of Mexico and connecting with the 
scrub, or chaparral, of northern Yucatan, whore the arboreal elements belong 
to the Leguminosae among which are species of Cassia, Acacia cornigera and 
others associated with Cereus peruvianus, C. flagelliformis and Cactus opuntia?). 
Forty years ago, it would never have occurred to one that this arid region 
of the Rio Grande could ever lay claim to being in any sense a wooded 
Country. Yet we see the spectacle of an invasion of chaparral, a horde of 
Shrubby Mexican species pushing their vanguard into the agricultural lands of 
the state. A journey of the writer some few years ago across Texas confırmed 
the fact that of these Mexican trees the mesquite (Prosrpis juliflora) is the 
dominant and strenuous species. Its spread northward and eastward by the 
Seeds voided in the feces of cattle from the Rio Grande country during the past 
ffty years has been a marked phenomenon. By its invasion, mile after mile 
of treeless plain and prairie have been won and reduced to the characteristic 
Orchard-like landscape. In the coast country, and likewise in the Black Prairie 
region, it has passed the Brazos River. It has pushed northward over the 
Staked plains, covering half their area. Along their eastern front, it has 
Migrated into Kansas and Oklahoma’). 
Tropic Forest. The tropic forest vegetation represents another important 
element in the flora of Mexico. It extends between the coastal chaparral and 
aid plateau on the upper and middle slopes of the mountains which 
!) Bray, WILLIAML.: The ecological Relation of the Vegetation of western Texas. Botanical 
Gazette XXXIT: 271. : 
A u CA. HEILPRIN, ANGELO: Observations on the Flora of northern Yucatan. Proceedings 
werican Philosophical Society XXIX: 137. 1891. ; 
ei 3) Brav, W.L.: Forest Resources of Texas. Bureau of Forestry U. S. Department of Agri- 
re. Balletin No. 47. 1904: 34. 
