8 FLORA OF ST. CROIX AND THE VIRGIN ISLANDS. 



partly also on the southern part of all tlie islands, a drj' shrubby vege- 

 tation of a gjeyish or yellowish aspect, which, from the predominating" 

 genus coiiii)()sinj;- its elciiicnts, 1 have called the Croton vegetation. This 

 l)eculiar kind of dry shrub also occurs here and there in other parts of 

 the islands, where the soil, through reckless cidtivation, has become too 

 exhausted to produce a growth of taller trees, and it cannot be estimated 

 to cover less than one third part of the whole surface of the islands, pre- 

 dominating in some, as Tortola, St. Thomas, and Oulebra, less conspicu- 

 ous in others, as St. Jan, Vieques, and St. Croix. 



The ravines as well as the northern and western parts of the islands 

 are often covered w'ith a growth of taller trees, forming a Idnd of forest, 

 composed of species partly evergreen and partly with deciduous foliage, 

 and Avhich, from one of the most prominent forms, 1 have called the Erio- 

 dendron vegetation. The area covered by this iorniation may be taken 

 to be about one fifth of the whole surface, the best wooded islands being 

 St. Jan and Vieques, the least wooded ones St. Thomas and Viigin 

 Gorda. 



The remainder of the surface is either used for pasture or cultivated 

 ■with sugar-cane or provisions, the former on a large scale iu St. Croix 

 and Vieques only, the latter everywhere on the islands where the soil 

 seems proper for the purpose. This last section 1 term the cultivated 

 region. 



Considering first the C/roton vegetation, we find here a number of plants 

 whieh in varions ways have become enabled to resist the deteritnating 

 eftects of the dry climate, and to exist on the barren rocky soil always 

 found where the moisture is not suflBcient for decojnposing the natnral 

 rock of the surface. Thus, some of these plants, as the whole of the 

 genus Croton, already mentioned above, have small leaves, wliich, like 

 the stem, are covered with scales and tomentose hair, eontaining besides 

 arouuitic oil, all which contrivances tend to diminish evaporation as nmcli 

 as possible. The most common species of tliis n niaikable genus are C. 

 flavufi, ((.stroitcfi, bicolor, and bctuliinis. Otlier forms obtain the same 

 object by liaving very small, partly deciduous leaves and their stii>ides 

 transfornie(l into ])riekles, especially the Acacia*, such as .1. Far)irxiana, 

 macracniillui, fortitosa, and aarmeniom. Others, again, are rich in milky 

 juice, as JJupliorbia pct'wlaria^ Ramcoljia LanKtrclii, an<l the natnralized 

 Calotropis prnccrn, or nunely in aqueous sap, as the Cactea^ the connnon- 

 est forms of whieh are ^f^■JtH'avtus communis^ Ccrcus form.suii, and several 

 species of < )i>unt ia. Others, such as Bronudiacea', on the contrary, have 



