332 Part III. Chapter 4. 
Antilles. On the west, the tropic elements pass vertically rather than gradually 
into the vegetation of the tierra templada of Mexico and Guatemala, and at 
the north, a semitropic Gulf strip from the mouth of the Rio Grande to and 
including upper Florida, marks the transition to the subtropic flora of the 
Gulf states which, though distinctiy a part of the Atlantic coast plain flora has 
numerous elements oftropic 
extraction as, for example, 
the Palmae, the Tillandsias 
(Fig. 18), some Euphorbia- 
ceae (Argithamnia, Aca- 
lypha, Sebastiana, Stillingia 
and Hippomane), Bignonia, 
Phoradendron, Persea and 
many others. 
At the west, the north- 
ward extension ofthe tropic 
flora is checked by xero- 
phytic conditions, so that 
a very meager tropic ele- 
ment reaches the United 
States in that quarter. On 
the other hand, the free 
northward extension to the 
Florida province, whose 
physical conditions favor 
a purely tropic flora, has 
been retarded by inter- 
ruptions in the continuity 
of the landmasses, so while 
the flora of south Florida is 
not a part of the Atlantic 
coastal plain flora and sub- 
tropic, it is comparatively 
meagerly provided with 
Fig. 13. Tillandsia usneoides L. Florid . 
an plant, festooning trees Be u. South American species. 
tropie coastal plains from Virginia to Texas and in Central ]t has, however, many 
America. After Die natürlichen Pflanzenfamilien IT4, p.56. elements in common with 
the Antilles. The sharp 
distinction between south Florida and the remaining Gulf states and north 
Florida, is shown in the following data compiled by DRUDE from CHAPMAN’S 
Flora. There are 360 species in Florida which do not extend north of the 
2gth parallel; of these 169 belong to 132 genera which have no distribution 
further northward, or ı6 families reach a northern limit in this peninsula. 
According to the discoveries of Dr. J. K. SMALL in the Miami neighborhood, 
N 
