FLORA OF THE GALAPAGOS ISLANDS. 237 



penetrate higher, moister strata of the air, and support a much more 

 hixii riant vegetation of a mesophytic type. Between these chief types 

 of vegetation there are perceptible but ill-defined belts of an intermediate 

 nature. A few lakes and ponds, some muddy and others briny, support 

 a littoral vegetation, chiefly of Cyperaceae, a family represented by sev- 

 enteen species and varieties of Cijperus and one or two each of Dichro- 

 tiema, Eleocharis, Funbristj/lis, Hemicarpha, KylUnga^ and Scleria. A 

 cold spring on Charles Island contains an Azolla (Andersson), and in 

 a small brook on the same island a Saloinia, a CalUtriche, and a Lemna 

 have been found (Wolf) ; but as both springs and streams are rare anil 

 small, such true hydrophytes are few and relatively unimportant in the 

 archipelago. Halophytes are more abundant, and occur not only on the 

 sandy beaches in the brackish marshes along the shore, but to some 

 extent around the saline lakes of the intei'ior portions of the islands. 

 The chief halophytes are Cissampelos Pareira, Tephrosm cinerea, 

 Rhizophora Mangle, Lnguncnlarla rac.emo$a, Sesuviiim Portidacastrum^ 

 S. Edmonstonei, Cah/stegia Soldanella, Tpomoea blloba, I. Haheliana, 

 Balls maritima, Avicennia ojficrnalls, Vei'hena lltoralis, Heliotropinm 

 curassavicum, Scaevola Lobelia, Ruppia 7narithnn, Najas marina, var. 

 latifolia, and probably Thliiogeton Mlersli, T. Hookeri, and two undeter- 

 mined species of Atrlplex. 



The lower arid slopes support not only the stemray, suffrutescent veg- 

 etation described above, but also are covered from time to time by an 

 ephemeral growth of desert annuals, which spring up shortly after the 

 rainy season begins, mature rapidly, and quickly dry up completely. 

 Examples of this type of plants are found in Porophyllum elUptlcum, 

 Ecolvulus simplex, an;l several species of Boerhaavia, Kallstroemia, 

 IVlbulus, and Bidens. 



Trees, if we except the arborescent cacti, occur chiefly upon the upper 

 parts of the islands and never attain great size. In many cases, however, 

 the same species which form a tree-like growth iu the upper region 

 extend well into the lower or even to the shore as shrubs, stunted by 

 the extreme drought and sterility of their environment. The trees 

 and shrubs are in great part armed with spines or tliorns, e.g. Mimosa, 

 Acacia, Parklnsonia, Discaria, Castela, Zanthoxi/lum, Cereus, and 

 Opuntla, — genera, all of which, it will be noticed, belong to the chori- 

 potalous dicotyledons. On the other hand, species protected by poisonous 

 juices or stinging hairs appear to be few. The climbing plants of the 

 islands are chiefly of the genera BousxinganUia, Cissampelos, Galaetea, 

 Rhgnchosia, Cardiospermnm, Fpomoea, Elaterium, Momordica, and Slcyos. 



