238 EVOLUTION OF PLANTS 
as the Gulf of Mexico is approached, is unfavorable for 
the growth of the strictly desert plants. With the 
increase in the rainfall, the desert gives place to a prairie 
formation, with coarse grasses and many showy flowers, 
phloxes, evening primroses, and gay Composite. Still 
further east the amount of moisture is sufficient for the 
growth of a few low-spreading trees like the “ mesquit” 
of the Texan plains, and in eastern Texas open forests 
of pines appear, which presently give way to the dense 
forests and swamps of the Gulf region of Louisiana. 
Here the conditions are almost tropical. An extremely 
heavy rainfall and high temperature combine to produce 
a rank vegetation, forming deep swamps and jungle-like 
forests. Very few of the plants occurring in these wet 
forests and swamps are at all related to the desert plants 
of the same latitude, but have their nearest allies among 
the plants of the Atlantic side of the continent. The 
eastern forests, unlike those of the Pacific slope, contain 
few Conifers, but there is a remarkable variety of 
angiospermous trees, most of which are deciduous. 
Hickories, gums, magnolias, tulip-trees, elms, beeches, 
and many other trees, quite absent from the Pacific 
coast, are important constituents of this magnificent 
forest flora, while the herbaceous plants associated with 
them are quite as diverse in character. Among the 
plants of the Gulf region are a number of genuine tropi- 
cal types, like the “Spanish moss,” the most northerly 
representative of the pineapple family, and the palmet- 
toes, the most northerly palms of the United States. 
California, owing to its peculiar topography, has the 
most varied flora of any region within the United States, 
and is extremely interesting in respect to the origin of 
