INTERPRETATION OF PHORADENDRON AND FURCR^A 653 



into the West Indies, nor have they passed from the islands into the 

 United States. A few very polymorphous species or scarcely segregable 

 groups of species, like 'T. latifolium" and 'T. rubrum," are common to 

 Brazil, Mexico, and the West Indies ; except for these, the insular species 

 are different from those of North America, and both differ from those of 

 South America. 



Have the insular species come from the northern or the southern main- 

 land, or both, or have they passed to the tropical mainland in either or 

 both directions and spread over it? As with Yucca aloifolia, it is not 

 necessary to assume a land connection for the dissemination of these 

 mistletoes. Even more than the baccate yuccas, they appear able to pass 

 ordinary barriers, for their seeds not only are contained in edible fruits, 

 but they are so viscidly adhesive as to be likely to be transported to con- 

 siderable distances by birds which feed on the berries. As a matter of 

 fact, the several species do not range over large regions, except for the 

 few cases noted; but these and, in general, groups of intimately related 

 species, occur in such a way as to lead one to believe that they may have 

 passed into the Greater Antilles from the west or into the Lesser Antilles 

 from South America. The greater part of the Antillean species appear 

 to me to possess South American affinities. 



Agave indicates Eelationship to a successively fragmented 



Antillean Bridge or Spur extending southeastward 



FROM Yucatan 



I have deferred until the end a discussion of the Agaveae. Its two 

 genera, apparently, are relatively modern. One (Furcrcea) appears to 

 center in South America, though it ranges from temperate Brazil to the 

 Mexican tableland; the other (Agave) centers in Mexico, but ranges from 

 Arizona to the Isthmus, extending across the continent in Mexico, and in 

 some equivocal forms it occurs in tropical Florida and in Venezuela and 

 Colombia. 



Both genera are found throughout the West Indies: Furcrcea in few 

 and rather similar species; Agave in many species of several very distinct 

 types. Furcrcea appears to have entered the islands chiefly from South 

 America. Agave is absent from South America except for a few species 

 confined to the extreme northern region, the Colombian part of which 

 show Costa Eican affinities. This genus appears to have penetrated the 

 West Indies from the Mexican or Central American side. 



Furcraeas and agaves frequently are bulbiferous. Their bulbils are 

 very tenacious of life ; there is no telling, therefore, how far a species may 



