FLORA OF THE GALAPAGOS ISLANDS. 237 



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

 luxuriant 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 Cyperus and one or two each of Dichro- 

 nema, Eleocharis, Fimbristylis, Hemicarpha, Kyllinga, and Scleria. A 

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

 a small brook on the same island a Salvinia, a Callitriche, and a Lemna 

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

 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 interior portions of the islands. 

 The chief halophytes are Clssam,pelos Pareira, Tephrosia cinerea, 

 Rhizophora Mangle, Laguncularia racemosa, Sesuvium Portulacastrum, 

 S. Edmonstonei, Calystegia Soldanella, Ipomoea biloba, I. Haheliana, 

 Bads maritima, Avicennia officinalis, Verbena litoralis, Heliotropium 

 curassavicum, Scaevola Lobelia, Ruppia maritima, Najas marina, var. 

 ladfolia, and probably Thinogeton Miersii, T. Hooheri, and two undeter- 

 mined species of Atriplex. 



The lower arid slopes support not only the stemmy, 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 ellipticum, 

 Evolvulus simplex, and several species of Boerhaavia, Kallstroemia, 

 Tribulus, 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 in 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 thorrts, e. g. Mimosa, 

 Acacia, Parkinsonia, Discaria, Castela, Zanthoxylum, Cereus, and 

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

 petalous 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 Boussingaultia, Cissampelos, Galactea, 

 Rhynchosia, Cardiospermum, Ipomoea, Elaterium, Momordica, and Sicyos. 



