INTERPRETATION OF AGAVE 655 



differ in proportion to the depth of the water barriers that separate their 

 islands and not merely in relation to the width of these barriers. 



Unless Agave is assumed to have originated in the West Indies, and 

 the problem of distribution and its present bearing would remain un- 

 changed if this scarcely plausible assumption were made, the genus must 

 have entered the islands from the mainland. The possibility that it 

 entered in two directions, through northern South America and also 

 Mexico or Central America, is not excluded. In the former case the 

 parent stock from the south would have given rise to the Caribsese and 

 Viviparae, and that from the north to the Antillanse and Antillares, with 

 their respective offshoots, the Bahaman^ and Inaguenses. The proba- 

 bility, however, is that it entered from the Central American region, and 

 that its greater groups were differentiated at a relatively early date. 



Either supposition calls for belief in an essentially continuous, though 

 not necessarily direct, land connection (perhaps broken at the present 

 Anegada Passage) between the islands and the continents, as well as 

 between the several islands; for as they exist today the agaves of even 

 adjacent islands do not pass back and forth. 



From what I know of the representatives of this genus in the West 

 Indies, I am compelled to believe that they were derived from the main- 

 land at some late Tertiary or early Quaternary time when islands and 

 continents were continuous; that then or subsequently they have spread 

 through the chain over continuous land; that this continuity was broken 

 by subsidence or fault when the very deep Anegada Passage was formed; 

 and that later subsidences have caused in succession the deeper and lesser 

 water gaps by which the Antilles are divided into groups successively 

 more and less distinct in their agave flora. 



These conclusions are in accord with some of the less sweeping indi- 

 cations afforded by the other groups that I have analyzed in detail, and 

 with the general interblending of northern and southern elements in the 

 Antillean flora ; and they are not necessarily in conflict with the negative 

 suggestion of a lack of land connection afforded by Quercus and the 

 Nolineae. They harmonize also with the fact indicated by Eggers, that 

 the greatest break between these elements occurs where the deepest and 

 presumably the oldest break in an Antillean bridge occurs, at the place 

 where the Anegada Passage separates the islands Saint Thomas and Saint 

 Croix, now under the flag of the United States. 



