FLORA OF ST. CROIX AND THE VIRGIN ISLANDS. 17 



others being only imperfect. Without expecting too much from this 

 circumstance, yet I feel confident that not few of the St. Croix plants, 

 apparently wanting in the Virgin group, may, by closer research, still 

 be discovered growing there on some of them, whilst, on the other hand, 

 I am equally confident that none, or scarcely any, of the Virgin Islands 7 

 species wanting in St. Croix will be found in the latter island. 



It may furthermore be observed that scarcely any of the St. Croix 

 species which I have given as being absent from the Virgin group are 

 common or widely distributed over the island, and so are not possessed 

 of any great faculty for conquering ground in the struggle for exist- 

 ence, for which reason some of them may not have been able to gain 

 admission on the much smaller surface of the Virgin Islands, or, having 

 obtained a footing, they may have lost it again by the later immigra- 

 tion of other species, now peculiar to the group compared with St. Croix, 

 many of which, as will be remembered, are gregarious, and gifted with 

 great facility for expanding themselves. 



A very few species form an exception as to the limited distribution in 

 St. Croix, Bacliaris Valilii, Cordia alba, and JEgipMla martinicensis, oc- 

 curring rather frequently in the island, but having as yet not been found 

 at all in the Virgin group, although they occur in several others of the 

 West India islands. I am not prepared to give a satisfactory explana- 

 tion of this fact at the present moment; but such isolated exceptions will 

 no doubt always be met with in the explanation of general phenomena,, 

 and most probably a more thorough investigation of vegetable biology 

 will at a future day afford a satisfactory explanation of such appar- 

 ently inconsistent facts. 



In drawing the necessary consequences of the above stated theory for 

 explaining the geographical distribution of vegetable species in St. Croix 

 and the Virgin Islands, it would thus appear necessary to conclude, for 

 instance, from the occurrence of Sabinea florida both in Porto Eico, the 

 Virgin Islands, and Dominica, but not in St. Croix, that the first-named 

 islands were still all connected, when the latter had already been sep- 

 arated from them and put into its present isolated position. A similar 

 inference might be drawn from the distribution of Malpighia Cnida, 

 whilst the occurrence of Acacia nudiflora would seem to prove a simi- 

 lar thing for Hayti, Porto Eico, and Antigua. 



It can, therefore, scarcely be presumed, as done by Prof. Grisebach 

 in his Geogr. Verbreitung der Pfl. Westmdiens, that the distribution 

 of species is regulated chiefly by geographical distances. A closer in- 

 vestigation of the flora of the various islands no doubt will confirm the 

 Bull. Nat. Mas. No. 13 2 



