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, Eleogharis, 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 Cissampelos Pareira, Tephrosia cinerea, 
Rhizophora Mangle, Laguneularia racemosa, Sesuvium Portulacastrum, 
S. Edmonstonei, Cal) lystegia Soldanella, Ipomoea biloba, I Habeliana, 
Batis maritima, Avicennia officinalis, Verbena litoralis, Heliotropium 
curassavieum, Seaevola Lobelia, Ruppia maritima, Najas marina, var. 
latifolia, and probably vhoapanieig Miersii, T. Hookeri, and two undeter- 
mined species of Atriplex, 
The lower arid slopes auieciee 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 elliptieum, 
Evolvulus simplex, and several species of Boerhaavia, seraoteliignan: 
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 teddies 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. he trees 
and shrubs are in great part armed with spines or thorns, e. g. Mimosa, 
Acacia, Parkinsonia, Discaria, Castela, Zanthorylum, Cereus, and 
puntia, — 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. 
