168 ORIGIN OF LIFE IN AMERICA 



the Antilles is generally believed to be due to accidental dis- 

 persal. The seeds of these plants are supposed to have been 

 conveyed to southern Florida from the West Indian Islands 

 by winds, ocean currents or migratory birds. Professor 

 Engler,* for instance, argues that a direct land connection 

 between the West Indies and North America by way of Florida 

 could never have eixsted, because the latter had been sub- 

 merged beneath the sea until the end of Tertiary times, 

 and that seeds are easily conveyed to Florida by the branch 

 of the Gulf Stream sweeping along the northern shore of 

 Cuba in a north-eastward direction, carrying quantities of 

 vegetable matter and often even tree trunks. Winds could 

 only transport such seeds that are specially adapted for long 

 flights. As regards migratory birds, which are popularly 

 believed to carry seeds to great distances in their crops 

 and among their feathers, it may be pointed out that 

 the main highway for birds travelling between the eastern 

 States and South America is by way of north-western 

 Florida and Cuba, and not by southern Florida. f If 

 birds had any special influence in the transport of seeds, not 

 the southern portion of Florida but the northern one should 

 show affinities in the flora with the West Indies. If the 

 resemblance in the vegetation of southern Florida and the 

 Antilles were mainly due to the Gulf Stream, we should expect 

 to find the most pronounced similarity between the two floras 

 among the strand plants of Florida. This is not the case. 

 The great majority of the flowering plants now known to be 

 common to the West Indies and North America occur in what 

 is called the " hummocks " of the southern extremity of 

 Florida. These hummocks consist of isolated groups of hard- 

 wood trees, shrubs and vines, and are scattered like islands 

 in the everglades and pine forests, instead of being surrounded 

 by the ocean. Moreover, the flora of southern Florida is by 

 no means exclusively West Indian in character. About forty 

 species of plants are peculiar to southern Florida, and over 

 twenty are found elsewhere only in Mexico. J 



* Engler, A., " Entwicklungsgeschichte d. Florengebiete," II, p. 215. 

 t Cooke, W. W., "New Facts about Migration of Birds," p. 376. 

 | Harshberger, J. W., " Floristic Elements of Eastern North America," 

 p. 612. 



