684 Part IV. Chapter 7. 
Coast Formations. Our information concerning the marine algae of 
Puerto Rico is due to the work of Dr. F. Hauck‘). The cays and inlets of 
the island are frequently bordered by mangrove vegetation. Presumably 
the same plants enter this formation as in other parts of the American tropics. 
— Presumably the Dune, River Bank, Salt Marsh, Swamp, Savanna 
and Arid Plain formations exist on this island, as in Santo Domingo and 
Cuba, because Puerto Rico has a similar topographic configuration. The Pine 
Formation, however, is absent. 
Chaparral Formation. The chaparral formation occupies the foothills bet- 
ween the southern front of the central mountains and the southern coast, a 
region which is comparatively arid. The wide playas and stream valleys of 
this country were once covered with large trees, a few scattered examples of 
which have been preserved, with the clearing of the land for sugar culture. 
The flora is markedly different from the mountain region, although there are 
a few species of trees in common. Low, shrubby, thorny leguminous trees 
(species of Acacia, etc.) covered by Spanish mosses (7illandsia) largely com- 
pose the vegetation. In the dry season, the landscape has a brownish color 
in contrast to the bright greens of the mountain forests. This formation is 
found, especially well developed on the coast hills between Ponce and Yauco. 
In this country, it is accompanied by a thick undergrowth of grass, approaching the 
condition of a savanna. The limestone summits of the hills, or cerros, west of Yauco are cove- 
red by a remarkable growth of chaparral, including a little fan palm Thrinax Ponceana, the Llume 
palm Adria attenuata, arborescent cacti, accompanied by thorny trees, the whole draped by 
Tillandsia2). — This formation occurs on the Island of Culebra which, as the altitude of the 
hills is not sufficient to condense the moisture as rain, is a dry island. Its forest is low and not 
very dense consisting of guayanilla (Bueida buceras), lignum vitae (Guajacum sanctum) as the 
largest trees, while cactuses abound in ten species of the genera Cereus, Pilocereus, Mammil- 
laria, Nopalea, Opuntia and a palm (Coccothrinax) and giant century plant (Agave) are found. 
Tropic Forest Formation. “The composition of this forest varies from que- 
brado°) to quebrado and the trees of south and west slopes present distinct 
differences from those of east and north exposures. But to a large extent the 
distribution of species is more or less an accident. Trees have grown wher- 
ever the many means of distribution have dropped the seeds and where they 
have found conditions suitable to their needs. It is rare to find trees of the 
same species in considerable numbers together, except perhaps a palm 
(Aerista monticola Cook) which is more or less gregarious in habit. Here and 
there 'single trees or little groups of trees found only in one spot are seen, 
as for example the mago, Hernandia sonora. On the whole, then, the forest 
growth of the island is far from uniform, although the causes which have 
brought about its local differentiation are for the most part not of a kind to 
afford a basis for classification into types. 
ı) Hauck, F.: Meeresalgen von Puerto Rico: see Bibliogr. p. 89 
. 89. 
2) Forest Conditions of Puerto Rico. The Forester V: 234. October 1899. 
3) Quebrado = ravine, gorge. 
