FREE INSTITUTE OF SCIENCE 
VEGETATION OF SOUTH FLORIDA 
87 
in the sand-pine forest. Of the plants with a striking xerophytic structure 
may be mentioned Opuntia austrina Small, with flat joints, two feet tall, and 
the Spanish-bayonet, Yucca aloifolia L. 
The herbaceous plants of the sandy soil as a third layer grow out of a leaf 
litter two inches thick which covers the forest floor beneath the pine trees. 
The two most common herbs collected by me at West Palm Beach on August 
10, 1911, were Polygonella polygama (Vent.) A. Gray and Afzelia pectinata 
(Pursh.) Kuntze, while on some waste material at the edge of the forest grew the 
balsam-apple, Momordica charantia L. The earth-star, Geaster sp., was found 
as an element of the fourth or ground layer of the forest. The white sand of 
the rosemary scrub formation is either covered with pine needles and other 
litter, or with plant growth. Here and there are bare stretches of white sand 
with several gray lichens forming part of the fourth layer. Three species of 
Cladonia, determined by Prof. Bruce Fink, are found. They are Cladonia 
sylvatica (L.) Hoffm., which grows in rounded, spongy cushions, Cladonia 
alpestris (L.) Rabenh., a fine gray lichen, and Cladonia leporina Fr., a coarse 
gray lichen. 
The vegetation of these ancient sand dunes is essentially xerophytic, be- 
cause the water, which falls as rain, rapidly percolates through the sand. The 
radiation of the sun is also quite intense, especially the noonday glare, and the 
wind action must be considerable, as the pine trees incline inland in some 
places at considerable angles. The soil of these sand hills is well adapted to 
the growth of the pineapple and some of the largest pineapple plantations in 
Florida are found in this region. A few plantations are of such size that small 
cars, drawn by mules and men on wooden tracks are used to collect the fruit 
from distant parts of the sandy fields. The pineapple is the crop for such 
areas and its cultivation is being extended rapidly, so that in time the natural 
forest of sand pine and associated vegetation will be cleared to make room 
for pineapple fields. 
SLASH-PINE (PINUS CARIBAEA) FORMATION 
The exposures of oölitic limestone, which we have named and described 
in the section on Geology, the Miami-Key West oölite, are covered in the 
main with the slash-pine tree, Pinus caribaea Morelet, which also extends much 
farther north on other types of soils. The outcrops of oölotic limestone extend 
