6 FLORA OF ST. CROIX AND THE VIRGIN ISLANDS. 



evaporated again by the action of the sun and the trade- wind combined. 

 It is not till May, when the increased quantity of rain is sufficient to 

 penetrate the parched soil, that its influence and effect upon vegetation 

 makes itself felt by renewed life and activity in all the various branches 

 of the vegetable kingdom in general. 



Looking at the vegetation of St. Croix and the Virgin Islands in its 

 generality, and without entering into details, we may consider it to be 

 identical, as a whole, showing the same main features, and naturally 

 divided into four distinct formations, as in most other West India 

 Islands, viz. the littoral, the shrubby, the sylvan, and the region of 

 cultivation, connected, of course, here and there by intermediate forma- 

 tions, but on the whole virtually distinct from different biological con- 

 ditions. 



Beginning with the littoral flora, we find along the coast in shallow 

 water a multitude of Alga3, among which are found some marine Phane- 

 rogams, especially the common Thalassia testudinum and Cymodocea 

 manatorum, and in less quantity the beautiful little HalopMla Baillonii, 

 a recently discovered Potamea, with oval delicate leaves, and growing 

 gregariously on the bottom of the sea in coarse gravel. The vegetation 

 of tropical seashores is of a very uniform character all over the world, 

 the physical conditions being similar on them all, and the migration 

 from one shore to another being exceedingly facilitated by the sea as 

 well as by birds, storms, and the action and intercourse of the inhab- 

 itants. Thus, the same species of littoral plants are found on nearly all 

 the West India islands, many of them also inhabitants of far distant 

 shores on the African and Asiatic continents, belonging to the cosmo- 

 politan and transoceanic species, a list of which was first prepared by 

 Eobert Brown, and afterwards augmented by A. DeCandolle, and which 

 seem to possess an extraordinary faculty for migration. According to 

 the different character of the coast, as sandy, rocky, or swampy, the 

 vegetation on it also assumes a different aspect. 



On the sandy shore, which is composed of a fine white gravel, con- 

 sisting principally of innumerable pieces of broken shells and corals, 

 and thus forming a thick layer of carbonate of lime, we see a luxurious 

 flora of trees, shrubs, and minor plants, which all, on account of the 

 underground water collecting from the hills above, generally have a 

 green appearance all the year round, even when the hills of the interior 

 present a withered aspect from want of rain. Among the trees grow- 

 ing here the most prominent are the Hippomane Mancinella, the Cocco- 



